From 6d48d7f852b3df5f6c18b0e9537861d915a4c64f Mon Sep 17 00:00:00 2001
From: Carm <carm@carm.cc>
Date: Tue, 20 Oct 2026 09:46:47 +0800
Subject: [PATCH] feat(i18n): Add runtime language packs and language switching
 (#1)

---
 .gitignore                                    |   6 +-
 README.md                                     |  23 +-
 README.zh-CN.md                               | 234 ++++++++++
 README.zh-TW.md                               |  23 +-
 src/STPViewer/AboutDialog.xaml                |  35 +-
 src/STPViewer/AboutDialog.xaml.cs             |  81 ++--
 src/STPViewer/App.xaml.cs                     |  20 +-
 .../Converters/EnumToBoolConverter.cs         |   4 +-
 src/STPViewer/Converters/FileNameConverter.cs |   2 +-
 src/STPViewer/Localization/LocExtension.cs    |  20 +
 src/STPViewer/MainWindow.xaml                 | 297 +++++++------
 src/STPViewer/MainWindow.xaml.cs              |  40 +-
 src/STPViewer/Models/FaceInfo.cs              |   6 +-
 src/STPViewer/Models/LanguageDefinition.cs    |  24 +
 src/STPViewer/Models/MeasureMode.cs           |  16 +-
 src/STPViewer/Models/MeasurementResult.cs     |  19 +-
 src/STPViewer/Models/UnitSystem.cs            |  12 +-
 src/STPViewer/STPViewer.csproj                |   6 +-
 src/STPViewer/Services/InterferenceService.cs |  42 +-
 src/STPViewer/Services/LocalizationService.cs | 158 +++++++
 src/STPViewer/Services/MeasurementService.cs  | 118 +++--
 src/STPViewer/Services/RigidAlign.cs          |  15 +-
 src/STPViewer/Services/SectionService.cs      |  10 +-
 src/STPViewer/Services/SettingsService.cs     |  11 +-
 src/STPViewer/Services/StepImportService.cs   | 146 +++---
 src/STPViewer/Services/StlExportService.cs    |  35 +-
 src/STPViewer/Services/StlMeshReader.cs       |  27 +-
 src/STPViewer/StlExportDialog.xaml            |  43 +-
 src/STPViewer/StlExportDialog.xaml.cs         |   2 +-
 .../ViewModels/MainViewModel.Drag.cs          |  30 +-
 .../ViewModels/MainViewModel.Export.cs        |  87 ++--
 .../ViewModels/MainViewModel.Gizmo.cs         |  61 ++-
 .../ViewModels/MainViewModel.Interference.cs  |  41 +-
 .../ViewModels/MainViewModel.Localization.cs  |  32 ++
 .../ViewModels/MainViewModel.Section.cs       |  76 ++--
 src/STPViewer/ViewModels/MainViewModel.cs     | 345 ++++++++-------
 .../ViewModels/ModelNodeViewModel.cs          |  83 ++--
 src/STPViewer/ViewModels/QuickBarViewModel.cs |  91 ++--
 .../ViewModels/StlExportViewModel.cs          |  25 +-
 src/STPViewer/i18n/en.json                    | 417 ++++++++++++++++++
 src/STPViewer/i18n/zh_cn.json                 | 417 ++++++++++++++++++
 src/STPViewer/i18n/zh_tw.json                 | 417 ++++++++++++++++++
 tools/SmokeTest/AlignTest.cs                  |  35 +-
 tools/SmokeTest/ClipTest.cs                   |  30 +-
 tools/SmokeTest/ExportTest.cs                 |  18 +-
 tools/SmokeTest/InterferenceTest.cs           |  26 +-
 tools/SmokeTest/LocalizationTest.cs           | 313 +++++++++++++
 tools/SmokeTest/MakeDxf.cs                    |   4 +-
 tools/SmokeTest/MakeStl.cs                    |   6 +-
 tools/SmokeTest/Program.cs                    |  13 +-
 tools/SmokeTest/StlExportTest.cs              |  43 +-
 tools/SmokeTest/TreeDump.cs                   |   2 +-
 52 files changed, 3119 insertions(+), 968 deletions(-)
 create mode 100644 README.zh-CN.md
 create mode 100644 src/STPViewer/Localization/LocExtension.cs
 create mode 100644 src/STPViewer/Models/LanguageDefinition.cs
 create mode 100644 src/STPViewer/Services/LocalizationService.cs
 create mode 100644 src/STPViewer/ViewModels/MainViewModel.Localization.cs
 create mode 100644 src/STPViewer/i18n/en.json
 create mode 100644 src/STPViewer/i18n/zh_cn.json
 create mode 100644 src/STPViewer/i18n/zh_tw.json
 create mode 100644 tools/SmokeTest/LocalizationTest.cs

diff --git a/.gitignore b/.gitignore
index 615753b..c50ced5 100644
--- a/.gitignore
+++ b/.gitignore
@@ -2,13 +2,13 @@
 bin/
 obj/
 publish/
-Publish/          # publish-winapp 打包產物（大小寫明確，Linux/CI 也忽略）
+Publish/          # publish-winapp output on case-sensitive systems
 *.user
 .vs/
 
-# AI 協作素材不入 git
+# Local development assets
 For_AI/
 
-# 客戶 CAD 料號檔不入 git（避免外流）；測試模型放 For_AI/
+# CAD samples are stored locally in For_AI/
 *.stp
 *.step
diff --git a/README.md b/README.md
index c0b425b..c363f4a 100644
--- a/README.md
+++ b/README.md
@@ -1,6 +1,6 @@
 # STPViewer
 
-[![English](https://img.shields.io/badge/English-2ea043.svg)](README.md) [![繁體中文](https://img.shields.io/badge/%E7%B9%81%E9%AB%94%E4%B8%AD%E6%96%87-lightgrey.svg)](README.zh-TW.md)
+[![English](https://img.shields.io/badge/English-2ea043.svg)](README.md) [![简体中文](https://img.shields.io/badge/%E7%AE%80%E4%BD%93%E4%B8%AD%E6%96%87-lightgrey.svg)](README.zh-CN.md) [![繁體中文](https://img.shields.io/badge/%E7%B9%81%E9%AB%94%E4%B8%AD%E6%96%87-lightgrey.svg)](README.zh-TW.md)
 
 > A Windows desktop 3D viewer for STP/STEP CAD files — multi-file import, assembly tree, and point / distance / edge / face / circle measurement. Built with C# .NET 8 WPF.
 
@@ -52,6 +52,7 @@ Open mechanical STEP parts for quick review and measurement without a heavyweigh
 - **Interference check** 🧩 — with 2+ visible files, checks **every pair**: red intersection curves + intersecting triangle-pair count, or the minimum gap (gap ≈ 0 means a fit/match; coplanar contact is not interference)
 - **Section plane** ✂ — X/Y/Z axis **or an arbitrary plane picked from 3 points on the model**; position slider + numeric input + flip; CPU mesh clipping (parallel, in the background), original geometry preserved (measurement stays exact)
 - **Units** — one-click mm ⇄ inch; existing measurements (list + 3D labels) convert live
+- **Language** — choose a language from **View → Language**; available languages come from the `i18n/` JSON files at startup, and your choice is remembered
 - **Export** — measurement results to CSV (UTF-8 BOM, no mojibake in Excel), a 2× PNG screenshot, and 📤 **STEP export**: writes all visible parts at their current aligned positions into a new STEP file (originals untouched)
 - **View** — right-button orbit, wheel zoom, middle-button pan, ViewCube; one-click **Iso / Front / Top / Right** views and an **orthographic ⇄ perspective** toggle
 - **Remembers your setup** — window size/position, unit choice and recent files persist across sessions; side panels are resizable
@@ -118,6 +119,7 @@ dotnet run --project tools/SmokeTest -- "path\to\model.stp"   # import + assembl
 dotnet run --project tools/SmokeTest -- --clip-test           # section clipping math
 dotnet run --project tools/SmokeTest -- --interference-test   # interference: intersect / separate / contact
 dotnet run --project tools/SmokeTest -- --align-test          # 3-point rigid-transform math
+dotnet run --project tools/SmokeTest -- --localization-test   # language resources and live switching
 dotnet run --project tools/SmokeTest -- --export-test in.stp out.stp  # STEP export round-trip
 ```
 
@@ -135,6 +137,24 @@ NuGet dependencies (restored automatically): `CADability`, `HelixToolkit.Wpf`, `
 
 ---
 
+## 🌐 Adding a Language
+
+The application scans `i18n/*.json` beside the executable at startup. Each file name without `.json` is the language ID (for example, `en.json` → `en`, `zh_cn.json` → `zh_cn`). The JSON root has a `key` for the name shown in the language menu and a `data` object that maps resource keys to translated text:
+
+```json
+{
+  "key": "Français",
+  "data": {
+    "Ui.Language": "Langue",
+    "Ui.Main.MenuImport": "📂 Importer…"
+  }
+}
+```
+
+Use `src/STPViewer/i18n/en.json` as the list of text keys, translate its `data` values, and save the new file as UTF-8 in `i18n/` beside the executable. Restart STPViewer to see the new language in the menu and Quick Bar. No recompilation is needed.
+
+---
+
 ## 📁 Project Structure
 
 ```
@@ -145,6 +165,7 @@ STPViewer/
 ├── src/STPViewer/
 │   ├── STPViewer.csproj       # net8.0-windows, UseWPF, single-source <Version>
 │   ├── MainWindow.xaml / .cs   # Layout + mouse-pick forwarding
+│   ├── i18n/                  # Language JSON files copied beside the executable
 │   ├── Models/                 # FaceInfo, MeasureMode, MeasurementResult, UnitSystem
 │   ├── Services/               # StepImport, Measurement, Interference, Section, RigidAlign, Settings
 │   └── ViewModels/             # MainViewModel (partial: Drag/Gizmo/Section/Interference/Export), ModelNodeViewModel
diff --git a/README.zh-CN.md b/README.zh-CN.md
new file mode 100644
index 0000000..ff677a8
--- /dev/null
+++ b/README.zh-CN.md
@@ -0,0 +1,234 @@
+# STPViewer
+
+[![English](https://img.shields.io/badge/English-lightgrey.svg)](README.md) [![简体中文](https://img.shields.io/badge/%E7%AE%80%E4%BD%93%E4%B8%AD%E6%96%87-2ea043.svg)](README.zh-CN.md) [![繁體中文](https://img.shields.io/badge/%E7%B9%81%E9%AB%94%E4%B8%AD%E6%96%87-lightgrey.svg)](README.zh-TW.md)
+
+> STP/STEP 3D 查看器（Windows 桌面程序，C# .NET 8 WPF）— 多文件导入、装配树、点/距离/边/面/圆测量。
+
+![version](https://img.shields.io/badge/version-0.5.0-blue.svg) ![platform](https://img.shields.io/badge/platform-Windows-0078D6.svg) ![.NET](https://img.shields.io/badge/.NET-8.0-512BD4.svg) ![UI](https://img.shields.io/badge/UI-WPF-blueviolet.svg)
+
+---
+
+## 📖 目录
+
+- [✨ 功能特性](#-功能特性)
+- [💻 系统需求](#-系统需求)
+- [📥 安装](#-安装)
+- [🚀 快速开始](#-快速开始)
+- [📚 使用指南](#-使用指南)
+- [🔨 从源代码构建](#-从源代码构建)
+- [📁 项目结构](#-项目结构)
+- [⚠️ 已知限制](#️-已知限制)
+- [🤝 贡献](#-贡献)
+- [📜 版本记录](#-版本记录)
+- [🙏 致谢](#-致谢)
+
+---
+
+## ✨ 功能特性
+
+快速打开机械零件 STEP 文件进行查看和测量，无需安装 SolidWorks / Creo 等大型 CAD 软件。
+
+- **多文件导入** — STEP / STL / DXF，工具栏导入（可多选）、拖放到窗口、命令行 `STPViewer.exe a.stp b.stl`，或最近文件下拉菜单（▾，最近 10 项）
+- **装配树** — STEP product structure 还原为树（组件→零件）；逐节点显示/隐藏、更改颜色（作用于子节点）、缩放至节点；文件层级可移除、开关轮廓边线；**按名称搜索过滤**；右键 **只显示此节点 / 反转显示 / 全部显示 / 计算体积与质心**；提示信息显示外形尺寸 L×W×H
+- **测量**（工具栏切换模式或快捷键，点击模型）：
+
+  | 模式 | 快捷键 | 输出 |
+  |---|---|---|
+  | 📍 点 | P | XYZ 坐标（自动吸附邻近 B-rep 顶点**或圆心**） |
+  | 📏 距离 | D | 两点直线距离 + ΔX/ΔY/ΔZ — 点击两个孔缘自动吸附**圆心**，可直接测量孔中心距 |
+  | 📐 边 | E | 直线长 / 曲线长 / 圆弧长 + 半径 |
+  | ⬛ 面 | F | 面积（网格近似）+ 曲面类型（平面法向量、圆柱半径/轴向） |
+  | ⭕ 圆 | C | 圆心 / 半径 / 直径 / 周长 |
+  | ∠ 角度 | A | 两面（法向量）/ 两条直线边的夹角 + 补角 |
+  | ⇔ 面距 | M | 面到面最短距离（网格近似）+ 最近点对 |
+  | ⚖ 体积 | （树右键） | 网格有符号体积 + 质心标记 + 外形尺寸（封闭实体） |
+  | ⤚ 对齐（两点） | | 点「要移动零件」一点 + 目标点 → 纯平移使两点贴合 |
+  | 🎯 对齐（三点） | | 源文件 3 点 + 目标文件 3 对应点 → 旋转+平移一次贴合 |
+
+  再次按下同一快捷键退出模式；**Esc** 先取消当前选择、再按退出模式。
+- **旋转** — 树面板选文件 + 工具栏 ↻X/↻Y/↻Z 绕中心 +90°（用于调整朝向，可重复旋转）
+- **拖动** 🖐 — 手形光标模式，左键按住零件沿屏幕平面拖动、放开定位（右键转视角不受影响）
+- **操作器** ⊹ — 树面板选文件 → XYZ 三色箭头 + 旋转环（Fusion 360 风格）；拖箭头沿该轴移动（与视角无关）、拖环绕轴转。永远浮在最上层、不被实体遮挡
+- **干涉检查** 🧩 — 2 个以上可见文件**两两配对**检查：相交时显示红色干涉交线 + 相交的三角形对数；无相交时报告最小间隙（gap≈0 即为配合，共面贴合不算干涉）
+- **剖面** ✂ — X/Y/Z 轴或**在模型上点 3 点定义任意平面**；位置滑块 + 数值输入 + 反向；CPU 网格裁切（背景平行运算），原始几何保留（测量仍精确）
+- **单位** — mm ⇄ inch 一键切换，已有测量（列表与 3D 标签）实时换算
+- **语言** — 在 **视图 → 语言** 中选择语言；启动时从 `i18n/` 的 JSON 文件读取可用语言，并记住你的选择
+- **导出** — 测量结果 CSV（UTF-8 BOM，Excel 中文不乱码）、3D 视图 2× PNG 截图、📤 **STEP 导出**：可见零件以当前对齐位置写成新 STEP 文件（源文件不动）
+- **视角** — 右键旋转、滚轮缩放、中键平移、ViewCube；一键 **等角/前/上/右** 标准视图与 **正交⇄透视** 切换
+- **设置保存** — 窗口位置和大小、单位、最近文件自动保存；左右面板可拖动调宽
+
+测量原则：边长、圆半径、角度取 **B-rep 精确值**；面积为三角网格求和近似（三角化精度根据模型尺寸自适应 0.02–0.5 mm）。
+
+---
+
+## 💻 系统需求
+
+| 项目 | 需求 |
+|------|------|
+| 操作系统 | Windows 10 / 11（x64） |
+| 运行环境 | .NET 8 Desktop Runtime（依赖框架版）— Portable 版则免装 |
+| 构建 SDK | .NET 8 SDK（仅从源代码构建时需要） |
+
+---
+
+## 📥 安装
+
+下载发布版直接执行，免安装。
+
+- **依赖框架版**（文件较小）：需 .NET 8 Desktop Runtime，执行 `STPViewer v0.5.0.exe`。
+- **Portable 版**（self-contained）：内置运行环境，免安装 / 无需管理员权限，执行 `STPViewer v0.5.0.exe`。
+
+或从源代码构建（见下）。
+
+```bash
+git clone https://github.com/ETWen/STPViewer.git
+cd STPViewer
+dotnet build STPViewer.sln
+```
+
+---
+
+## 🚀 快速开始
+
+```bash
+# 构建并执行
+dotnet build STPViewer.sln
+dotnet run --project src/STPViewer
+
+# 发布免安装文件夹
+dotnet publish src/STPViewer -c Release -o publish/STPViewer
+```
+
+然后导入 `.stp` 文件（工具栏「导入」、拖放或命令行传入文件路径），选一个测量模式，点击模型即可。
+
+---
+
+## 📚 使用指南
+
+1. **导入** 一个或多个 CAD 文件，每个文件成为装配树的一个根节点，视角自动缩放至适合窗口。
+2. **操作树** — 按名称搜索、显示/隐藏（或右键隔离显示）、换色、缩放至某节点，或移除文件。
+3. **测量** — 在工具栏选择模式或按快捷键（P/D/E/F/C/A/M），点击模型；点击孔缘自动吸附圆心，点击两次即可测得孔中心距；Esc 取消。结果显示在右侧面板，可逐条删除或全部清除。
+4. **装配** — 使用对齐（两点/三点）、旋转、拖动、操作器摆位，再用干涉检查对所有可见文件两两检查，验证装配配合。
+5. **剖面** — 打开 ✂、选轴向或点 3 点定义任意平面、滑动（或输入 %）剖切；测量仍以原始几何精确计算。
+6. **导出** — 测量结果保存为 CSV、截取 2× PNG，或把对齐后的场景写成新 STEP 文件交接给 CAD。
+
+无需启动界面的导入流程与几何运算验证：
+
+```bash
+dotnet run --project tools/SmokeTest -- "path\to\model.stp"   # 导入 + 装配树
+dotnet run --project tools/SmokeTest -- --clip-test           # 剖切裁切数学
+dotnet run --project tools/SmokeTest -- --interference-test   # 干涉 相交/分离/贴合
+dotnet run --project tools/SmokeTest -- --align-test          # 三点对齐刚体变换数学
+dotnet run --project tools/SmokeTest -- --localization-test   # 语言资源与实时切换
+dotnet run --project tools/SmokeTest -- --export-test in.stp out.stp  # STEP 导出往返验证
+```
+
+---
+
+## 🔨 从源代码构建
+
+```bash
+dotnet build STPViewer.sln -c Debug
+dotnet run --project src/STPViewer
+dotnet publish src/STPViewer -c Release -o publish/STPViewer
+```
+
+NuGet 依赖（自动还原）：`CADability`、`HelixToolkit.Wpf`、`CommunityToolkit.Mvvm`。
+
+---
+
+## 🌐 添加语言
+
+程序启动时扫描可执行文件旁的 `i18n/*.json`。文件名去掉 `.json` 后就是语言 ID，例如 `en.json` 对应 `en`，`zh_cn.json` 对应 `zh_cn`。JSON 顶层的 `key` 是语言菜单中的显示名，`data` 是资源键到译文的映射：
+
+```json
+{
+  "key": "Français",
+  "data": {
+    "Ui.Language": "Langue",
+    "Ui.Main.MenuImport": "📂 Importer…"
+  }
+}
+```
+
+参考 `src/STPViewer/i18n/en.json` 中的资源键，翻译其 `data` 内容，将新文件以 UTF-8 编码放入可执行文件旁的 `i18n/`。重启 STPViewer 后，新语言便会出现在菜单和快捷栏中，无需重新编译。
+
+---
+
+## 📁 项目结构
+
+```
+STPViewer/
+├── ARCHITECTURE.md            # 设计、数据流、开发 阶段
+├── CLAUDE.md                  # 项目记忆 & 开发规范
+├── STPViewer.sln
+├── src/STPViewer/
+│   ├── STPViewer.csproj       # net8.0-windows、UseWPF、统一的版本号来源 <Version>
+│   ├── MainWindow.xaml / .cs   # 布局 + 鼠标拾取转发
+│   ├── i18n/                  # 复制到可执行文件旁的语言 JSON 文件
+│   ├── Models/                 # FaceInfo、MeasureMode、MeasurementResult、UnitSystem
+│   ├── Services/               # StepImport、Measurement、Interference、Section、RigidAlign、Settings
+│   └── ViewModels/             # MainViewModel（partial：Drag/Gizmo/Section/Interference/Export）、ModelNodeViewModel
+└── tools/SmokeTest/           # 无需 UI 导入 + 几何数学验证
+```
+
+---
+
+## ⚠️ 已知限制
+
+- 大型 STEP（数千面）导入需数十秒（CADability 解析成本），导入期间有进度提示、UI 不会卡住。
+- 轮廓边线超过 30,000 线段的文件会默认关闭边线（WPF `LinesVisual3D` 转动视角时性能限制），可在树面板手动打开。
+- **IGES 不支持**（CADability 无 IGES reader）；STL 无 B-rep，仅支持 点/距离/角度/面距 测量；DXF 为线框查看。
+- 剖切面无封口（cap），剖开处显示内部背面材质（深灰）。
+- STEP 导出为「当前位置的 Solid/Shell 扁平列表」，不保留原始装配层级与 product 名称；STL 网格、DXF 线框无 B-rep 不导出。
+- 面积、面距、体积/质心为三角网格近似值；边长/圆半径/角度为 B-rep 精确值。
+- 少数 AP242 文件 CADability 支持不完整，导入失败会提示消息（不会崩溃）。
+- 只读查看器，不写入/修改原始文件。
+
+---
+
+## 🤝 贡献
+
+1. Fork 并建立 feature 分支：`git checkout -b feature/your-feature`
+2. 遵循 [Conventional Commits](https://www.conventionalcommits.org/)：`feat(scope): summary`
+3. Push 后开 Pull Request
+
+---
+
+## 📜 版本记录
+
+### v0.5.0
+
+- **功能扩展：** 圆心吸附（点击两次测量孔中心距）、测量快捷键（P/D/E/F/C/A/M）+ Esc、标准视图（等角/前/上/右）+ 正交投影、装配树搜索/隔离显示/反转、体积与质心、3 点任意剖切平面 + 位置数值输入、干涉检查支持 3 个以上文件（两两配对）、对齐后场景导出 STEP、面板可调宽、窗口/单位/最近文件自动保存。
+
+### v0.4.0
+
+- **性能：** 剖面裁切改为后台并行运算（大文件拖动滑块时不再卡住 UI）；零件变换烘焙（拖动/操作器放开）并行化；干涉间隙精修以 AABB 快速排除加速。
+- **稳定性：** 全域例外处理（记 log 至 `%LOCALAPPDATA%\STPViewer\error.log` + 消息框，不会崩溃）；背景运算期间停用会改动几何的指令；导入防重入。
+
+### v0.3.2
+
+- **性能：** 大组件测量模式下转动视角不再卡顿。测量模式改为渲染合并网格（每个文件 1 个 model），并用命中三角形的顶点 index 反查回是哪个面，不再挂数万个逐面 model；逐面渲染只保留给剖面模式。
+- 相机交互暂停事件额外监听 `HelixViewport3D.CameraChanged`，避免相机实例被换掉时失去订阅。
+
+### v0.3.1
+
+- 操作器 always-on-top 叠图层（永远浮在零件上、不被实体遮挡）。
+
+### v0.3.0
+
+- 旋转对齐：轴向旋转（↻X/↻Y/↻Z）、三点对齐，以及统一的 `TransformRoot` 刚体变换路径。
+
+### v0.2.x
+
+- 拖动模式、两点对齐、干涉检查、剖面、角度/面距测量、装配树、STL/DXF 支持、mm ⇄ inch。
+
+---
+
+## 🙏 致谢
+
+- [CADability](https://github.com/SOFAgh/CADability) — 纯 C# CAD kernel：STEP 导入、B-rep 几何、面三角化
+- [HelixToolkit.Wpf](https://github.com/helix-toolkit/helix-toolkit) — 3D viewport、相机操作、HitTest
+- [CommunityToolkit.Mvvm](https://github.com/CommunityToolkit/dotnet) — MVVM
+
+详细设计与开发 阶段 见 [ARCHITECTURE.md](ARCHITECTURE.md)。
diff --git a/README.zh-TW.md b/README.zh-TW.md
index 3e0604b..6f607a4 100644
--- a/README.zh-TW.md
+++ b/README.zh-TW.md
@@ -1,6 +1,6 @@
 # STPViewer
 
-[![English](https://img.shields.io/badge/English-lightgrey.svg)](README.md) [![繁體中文](https://img.shields.io/badge/%E7%B9%81%E9%AB%94%E4%B8%AD%E6%96%87-2ea043.svg)](README.zh-TW.md)
+[![English](https://img.shields.io/badge/English-lightgrey.svg)](README.md) [![简体中文](https://img.shields.io/badge/%E7%AE%80%E4%BD%93%E4%B8%AD%E6%96%87-lightgrey.svg)](README.zh-CN.md) [![繁體中文](https://img.shields.io/badge/%E7%B9%81%E9%AB%94%E4%B8%AD%E6%96%87-2ea043.svg)](README.zh-TW.md)
 
 > STP/STEP 3D 檢視器（Windows 桌面程式，C# .NET 8 WPF）— 多檔匯入、裝配樹、點/距離/邊/面/圓量測。
 
@@ -52,6 +52,7 @@
 - **干涉檢查** 🧩 — 2 個以上可見檔案**兩兩配對**檢查：相交時顯示紅色干涉交線 + 相交三角形對數；無相交時回報最小間隙 gap（gap≈0 即為配合 match，共面貼合不算干涉）
 - **剖面** ✂ — X/Y/Z 軸或**在模型上點 3 點定義任意平面**；位置滑桿 + 數值輸入 + 反向；CPU 網格裁切（背景平行運算），原始幾何保留（量測仍精確）
 - **單位** — mm ⇄ inch 一鍵切換，既有量測（清單與 3D 標籤）即時換算
+- **語言** — 從 **視圖 → 語言** 選擇語言；啟動時從 `i18n/` 的 JSON 檔案讀取可用語言，並記住選擇
 - **匯出** — 量測結果 CSV（UTF-8 BOM，Excel 中文不亂碼）、3D 視圖 2× PNG 截圖、📤 **STEP 匯出**：可見零件以目前對齊位置寫成新 STEP 檔（原始檔不動）
 - **視角** — 右鍵旋轉、滾輪縮放、中鍵平移、ViewCube；一鍵 **等角/前/上/右** 標準視圖與 **正交⇄透視** 切換
 - **記住設定** — 視窗位置大小、單位、最近檔案自動保存；左右面板可拖曳調寬
@@ -118,6 +119,7 @@ dotnet run --project tools/SmokeTest -- "path\to\model.stp"   # 匯入 + 裝配
 dotnet run --project tools/SmokeTest -- --clip-test           # 剖切裁切數學
 dotnet run --project tools/SmokeTest -- --interference-test   # 干涉 相交/分離/貼合
 dotnet run --project tools/SmokeTest -- --align-test          # 三點對齊剛體變換數學
+dotnet run --project tools/SmokeTest -- --localization-test   # 語言資源與即時切換
 dotnet run --project tools/SmokeTest -- --export-test in.stp out.stp  # STEP 匯出往返驗證
 ```
 
@@ -135,6 +137,24 @@ NuGet 相依（自動還原）：`CADability`、`HelixToolkit.Wpf`、`CommunityT
 
 ---
 
+## 🌐 新增語言
+
+程式啟動時掃描執行檔旁的 `i18n/*.json`。檔名去掉 `.json` 後就是語言 ID，例如 `en.json` 對應 `en`，`zh_tw.json` 對應 `zh_tw`。JSON 頂層的 `key` 是語言選單中的顯示名稱，`data` 是資源鍵與譯文的對應：
+
+```json
+{
+  "key": "Français",
+  "data": {
+    "Ui.Language": "Langue",
+    "Ui.Main.MenuImport": "📂 Importer…"
+  }
+}
+```
+
+參考 `src/STPViewer/i18n/en.json` 的資源鍵，翻譯其 `data` 內容，將新檔案以 UTF-8 編碼放入執行檔旁的 `i18n/`。重啟 STPViewer 後，新語言便會出現在選單與快速列中，不需重新編譯。
+
+---
+
 ## 📁 專案結構
 
 ```
@@ -145,6 +165,7 @@ STPViewer/
 ├── src/STPViewer/
 │   ├── STPViewer.csproj       # net8.0-windows、UseWPF、單一版號來源 <Version>
 │   ├── MainWindow.xaml / .cs   # 版面 + 滑鼠拾取轉發
+│   ├── i18n/                  # 複製到執行檔旁的語言 JSON 檔
 │   ├── Models/                 # FaceInfo、MeasureMode、MeasurementResult、UnitSystem
 │   ├── Services/               # StepImport、Measurement、Interference、Section、RigidAlign、Settings
 │   └── ViewModels/             # MainViewModel（partial：Drag/Gizmo/Section/Interference/Export）、ModelNodeViewModel
diff --git a/src/STPViewer/AboutDialog.xaml b/src/STPViewer/AboutDialog.xaml
index b131a4d..e257666 100644
--- a/src/STPViewer/AboutDialog.xaml
+++ b/src/STPViewer/AboutDialog.xaml
@@ -1,7 +1,8 @@
 <Window x:Class="STPViewer.AboutDialog"
         xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
         xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
-        Title="關於 STPViewer"
+        xmlns:loc="clr-namespace:STPViewer.Localization"
+        Title="{loc:Loc Ui.About.Title}"
         Width="860" Height="600"
         WindowStartupLocation="CenterOwner"
         ResizeMode="CanResize" MinWidth="700" MinHeight="420"
@@ -34,7 +35,7 @@
             <RowDefinition Height="Auto" />
         </Grid.RowDefinitions>
 
-        <!-- ─── 左：程式 / 開發者 / 技術棧 ─── -->
+        <!-- Application, developer, and technology -->
         <StackPanel Grid.Column="0" Grid.Row="0" Margin="0,0,12,0">
             <Border Style="{StaticResource Card}">
                 <StackPanel HorizontalAlignment="Center">
@@ -42,17 +43,14 @@
                                Foreground="#1565C0" HorizontalAlignment="Center" />
                     <TextBlock x:Name="VersionText" Text="v0.0.0" Style="{StaticResource DimText}"
                                HorizontalAlignment="Center" Margin="0,2,0,8" />
-                    <TextBlock TextAlignment="Center" FontSize="12" LineHeight="18">
-                        STP / STEP 3D 檢視器<LineBreak />
-                        免開重量級 CAD，快速開檔、量測、<LineBreak />
-                        對齊插合、干涉檢查、剖面、匯出
-                    </TextBlock>
+                    <TextBlock Text="{loc:Loc Ui.About.Description}" TextAlignment="Center"
+                               TextWrapping="Wrap" Width="260" FontSize="12" LineHeight="18" />
                 </StackPanel>
             </Border>
 
             <Border Style="{StaticResource Card}">
                 <StackPanel>
-                    <TextBlock Text="👤  開發者" Style="{StaticResource CardTitle}" />
+                    <TextBlock Text="{loc:Loc Ui.About.Developer}" Style="{StaticResource CardTitle}" />
                     <Grid>
                         <Grid.ColumnDefinitions>
                             <ColumnDefinition Width="60" />
@@ -61,9 +59,9 @@
                         <Grid.RowDefinitions>
                             <RowDefinition /><RowDefinition /><RowDefinition />
                         </Grid.RowDefinitions>
-                        <TextBlock Grid.Row="0" Grid.Column="0" Text="Name" Style="{StaticResource DimText}" />
+                        <TextBlock Grid.Row="0" Grid.Column="0" Text="{loc:Loc Ui.About.Name}" Style="{StaticResource DimText}" />
                         <TextBlock Grid.Row="0" Grid.Column="1" Text="ET Wen" FontSize="12" />
-                        <TextBlock Grid.Row="1" Grid.Column="0" Text="Email" Style="{StaticResource DimText}" />
+                        <TextBlock Grid.Row="1" Grid.Column="0" Text="{loc:Loc Ui.About.Email}" Style="{StaticResource DimText}" />
                         <TextBlock Grid.Row="1" Grid.Column="1" Text="eric441151893@gmail.com" FontSize="12" />
                         <TextBlock Grid.Row="2" Grid.Column="0" Text="GitHub" Style="{StaticResource DimText}" />
                         <TextBlock Grid.Row="2" Grid.Column="1" Text="github.com/ETWen" FontSize="12" />
@@ -73,27 +71,24 @@
 
             <Border Style="{StaticResource Card}">
                 <StackPanel>
-                    <TextBlock Text="🔧  技術棧" Style="{StaticResource CardTitle}" />
-                    <TextBlock Style="{StaticResource DimText}" LineHeight="18">
-                        .NET 8 · WPF · C#<LineBreak />
-                        CADability（STEP / B-rep 幾何核心）<LineBreak />
-                        HelixToolkit（3D 顯示與相機）
-                    </TextBlock>
+                    <TextBlock Text="{loc:Loc Ui.About.TechnologyTitle}" Style="{StaticResource CardTitle}" />
+                    <TextBlock Text="{loc:Loc Ui.About.Technology}" Style="{StaticResource DimText}"
+                               TextWrapping="Wrap" Width="260" LineHeight="18" />
                 </StackPanel>
             </Border>
         </StackPanel>
 
-        <!-- ─── 右：Change log ─── -->
+        <!-- Release history -->
         <Border Grid.Column="1" Grid.Row="0" Background="#FAFBFC" CornerRadius="6" Padding="4">
             <DockPanel>
-                <TextBlock DockPanel.Dock="Top" Text="📋  版本紀錄" FontWeight="Bold" FontSize="14"
+                <TextBlock DockPanel.Dock="Top" Text="{loc:Loc Ui.About.Changelog}" FontWeight="Bold" FontSize="14"
                            Margin="12,8,0,4" />
                 <ScrollViewer VerticalScrollBarVisibility="Auto" Padding="12,0,12,8">
                     <ItemsControl x:Name="ChangelogList">
                         <ItemsControl.ItemTemplate>
                             <DataTemplate>
                                 <StackPanel Margin="0,8,0,4">
-                                    <TextBlock FontWeight="Bold" Foreground="#1565C0" FontSize="13">
+                                    <TextBlock FontWeight="Bold" Foreground="#1565C0" FontSize="13" TextWrapping="Wrap">
                                         <Run Text="●" /> <Run Text="{Binding Header, Mode=OneWay}" />
                                     </TextBlock>
                                     <ItemsControl ItemsSource="{Binding Changes}" Margin="16,3,0,0">
@@ -112,7 +107,7 @@
             </DockPanel>
         </Border>
 
-        <Button Grid.Column="1" Grid.Row="1" Content="關閉" Width="90" Margin="0,10,0,0"
+        <Button Grid.Column="1" Grid.Row="1" Content="{loc:Loc Ui.About.Close}" Width="90" Margin="0,10,0,0"
                 HorizontalAlignment="Right" IsCancel="True" IsDefault="True" />
     </Grid>
 </Window>
diff --git a/src/STPViewer/AboutDialog.xaml.cs b/src/STPViewer/AboutDialog.xaml.cs
index 2ef61ea..7a36572 100644
--- a/src/STPViewer/AboutDialog.xaml.cs
+++ b/src/STPViewer/AboutDialog.xaml.cs
@@ -2,12 +2,13 @@ using System;
 using System.Linq;
 using System.Reflection;
 using System.Windows;
+using STPViewer.Services;
 
 namespace STPViewer;
 
 /// <summary>
-/// 關於視窗：左 = 程式資訊 / 開發者 / 技術棧，右 = 版本紀錄（寫給一般使用者看，非技術 changelog）。
-/// 樣式參考 ETTerms 的 AboutView。發新版時在 Changelog 陣列最上面加一筆。
+/// The About window shows application information on the left and release history on the right.
+/// Add each new release at the start of Changelog.
 /// </summary>
 public partial class AboutDialog : Window
 {
@@ -18,80 +19,80 @@ public partial class AboutDialog : Window
         VersionText.Text = $"v{v.Major}.{v.Minor}.{v.Build}";
         ChangelogList.ItemsSource = Changelog.Select(e => new
         {
-            Header = $"v{e.Version}  ·  {e.Title}    ({e.Date:yyyy-MM-dd})",
-            e.Changes,
+            Header = $"v{e.Version}  ·  {LocalizationService.Get(e.Title)}    ({e.Date:yyyy-MM-dd})",
+            Changes = e.Changes.Select(LocalizationService.Get).ToArray(),
         }).ToList();
     }
 
     private record ChangelogEntry(string Version, DateOnly Date, string Title, string[] Changes);
 
-    // ── 版本紀錄（新版加最上面；口吻：一般使用者看得懂，講「你會感覺到什麼」而非實作細節）──
+    // Release history shown to users, newest first.
     private static readonly ChangelogEntry[] Changelog =
     {
-        new("0.7.1", new DateOnly(2026, 7, 12), "大型 STL 秒開",
+        new("0.7.1", new DateOnly(2026, 7, 12), "Ui.About.Release071.Title",
         new[]
         {
-            "• 開啟大型 STL 網格檔（數十 MB、上百萬三角形）現在幾乎瞬間完成，不用再等好幾分鐘。",
-            "• 例如一個 75 MB、150 萬個三角形的 STL，以前要等到天荒地老，現在不到 1 秒就顯示出來。",
+            "Ui.About.Release071.Change1",
+            "Ui.About.Release071.Change2",
         }),
-        new("0.7.0", new DateOnly(2026, 7, 4), "介面大整理 — 選單列＋可自訂快速列",
+        new("0.7.0", new DateOnly(2026, 7, 4), "Ui.About.Release070.Title",
         new[]
         {
-            "• 上方新增選單列，全部功能依「檔案／視圖／量測／變換／工具」分類，不用再在一長排按鈕裡找。",
-            "• 原本的工具列變成「快速列」：只放常用按鈕。想放哪些自己決定 — 到「快速列 → 自訂按鈕」勾選，下次開啟會記住。",
-            "• 剖面的軸向／位置控制列改成只在開啟剖面時出現，平常不佔空間。",
-            "• 新增「關於」視窗（就是這個畫面），可以看版本紀錄。",
+            "Ui.About.Release070.Change1",
+            "Ui.About.Release070.Change2",
+            "Ui.About.Release070.Change3",
+            "Ui.About.Release070.Change4",
         }),
-        new("0.6.0", new DateOnly(2026, 7, 4), "匯出 STL",
+        new("0.6.0", new DateOnly(2026, 7, 4), "Ui.About.Release060.Title",
         new[]
         {
-            "• 新增匯出 STL：把畫面上的零件（含對齊、旋轉後的位置）存成 STL 網格檔，可拿去 3D 列印或給其他軟體用。",
-            "• 匯出前會先跳出設定視窗：全部合併成一個檔或每個檔案各存一個、Binary 或文字格式、mm 或 inch、網格精細度 — 確認後才匯出。",
-            "• 設定視窗會即時顯示三角形數量與預估檔案大小。",
+            "Ui.About.Release060.Change1",
+            "Ui.About.Release060.Change2",
+            "Ui.About.Release060.Change3",
         }),
-        new("0.5.0", new DateOnly(2026, 7, 3), "量測、視圖、樹狀面板大升級",
+        new("0.5.0", new DateOnly(2026, 7, 3), "Ui.About.Release050.Title",
         new[]
         {
-            "• 量距離時點到圓孔邊緣會自動吸到圓心 — 量兩孔中心距（pitch）超方便。",
-            "• 量測快速鍵：P 點、D 距離、E 邊、F 面、C 圓、A 角度、M 面距；Esc 取消。",
-            "• 樹狀面板可搜尋零件名稱；右鍵可「只顯示此節點」隔離觀察，也可以量體積與質心。",
-            "• 新增標準視圖（等角／前／上／右）與正交投影，量尺寸不受透視變形。",
-            "• 剖面新增「3點」模式：在模型上點 3 個點，就能沿任意斜面剖開。",
-            "• 新增匯出 STEP：把對齊好的零件位置存成新 STEP 檔，交接給正式 CAD。",
-            "• 會記住視窗大小、單位設定與最近開啟的 10 個檔案。",
+            "Ui.About.Release050.Change1",
+            "Ui.About.Release050.Change2",
+            "Ui.About.Release050.Change3",
+            "Ui.About.Release050.Change4",
+            "Ui.About.Release050.Change5",
+            "Ui.About.Release050.Change6",
+            "Ui.About.Release050.Change7",
         }),
-        new("0.4.0", new DateOnly(2026, 7, 2), "更快、更穩",
+        new("0.4.0", new DateOnly(2026, 7, 2), "Ui.About.Release040.Title",
         new[]
         {
-            "• 大檔案拉剖面滑桿不再卡住畫面（改到背景計算）。",
-            "• 拖曳／操作器放開零件後的定位計算大幅加速。",
-            "• 程式遇到錯誤會提示訊息並繼續運作，不再整個閃退。",
+            "Ui.About.Release040.Change1",
+            "Ui.About.Release040.Change2",
+            "Ui.About.Release040.Change3",
         }),
-        new("0.3.2", new DateOnly(2026, 6, 18), "大組件量測不再卡",
+        new("0.3.2", new DateOnly(2026, 6, 18), "Ui.About.Release032.Title",
         new[]
         {
-            "• 修正大型組件（數萬個面）進入量測模式後，轉動視角嚴重卡頓的問題 — 現在量測跟瀏覽一樣順。",
+            "Ui.About.Release032.Change1",
         }),
-        new("0.3.1", new DateOnly(2026, 6, 13), "操作器永遠可見",
+        new("0.3.1", new DateOnly(2026, 6, 13), "Ui.About.Release031.Title",
         new[]
         {
-            "• 三軸操作器改成永遠浮在畫面最上層，不會被零件擋住，任何角度都抓得到。",
+            "Ui.About.Release031.Change1",
         }),
-        new("0.3.0", new DateOnly(2026, 6, 13), "三軸操作器",
+        new("0.3.0", new DateOnly(2026, 6, 13), "Ui.About.Release030.Title",
         new[]
         {
-            "• 新增操作器：選取檔案後出現 XYZ 三色箭頭與旋轉環，箭頭沿軸精確移動、旋轉環繞軸轉任意角度。",
+            "Ui.About.Release030.Change1",
         }),
-        new("0.2.0", new DateOnly(2026, 6, 13), "拖曳模式",
+        new("0.2.0", new DateOnly(2026, 6, 13), "Ui.About.Release020.Title",
         new[]
         {
-            "• 新增拖曳模式：左鍵按住零件直接拖到想要的位置，放開就定位。",
-            "• 0.2.1 修正拖曳過的零件再點擊會當掉的問題。",
+            "Ui.About.Release020.Change1",
+            "Ui.About.Release020.Change2",
         }),
-        new("0.1.0", new DateOnly(2026, 6, 13), "首次釋出",
+        new("0.1.0", new DateOnly(2026, 6, 13), "Ui.About.Release010.Title",
         new[]
         {
-            "• STEP／STL／DXF 匯入與裝配樹、點／距離／邊／面／圓／角度／面距量測、兩點與三點對齊、干涉檢查、剖面、mm ⇄ inch、CSV 與截圖匯出。",
+            "Ui.About.Release010.Change1",
         }),
     };
 }
diff --git a/src/STPViewer/App.xaml.cs b/src/STPViewer/App.xaml.cs
index 0f48b50..2f087bb 100644
--- a/src/STPViewer/App.xaml.cs
+++ b/src/STPViewer/App.xaml.cs
@@ -3,12 +3,13 @@ using System.IO;
 using System.Text;
 using System.Threading.Tasks;
 using System.Windows;
+using STPViewer.Services;
 
 namespace STPViewer;
 
 /// <summary>
-/// 全域例外處理：UI 執行緒未攔截例外 → 記 log + 訊息框後盡量存活（不閃退）；
-/// 背景 Task / 非 UI 執行緒例外 → 記 log。log 位於 %LOCALAPPDATA%\STPViewer\error.log。
+/// Log unhandled UI and background exceptions to
+/// %LOCALAPPDATA%\STPViewer\error.log and show a message for UI errors.
 /// </summary>
 public partial class App : Application
 {
@@ -18,28 +19,27 @@ public partial class App : Application
 
     protected override void OnStartup(StartupEventArgs e)
     {
+        LocalizationService.Instance.SetLanguage(SettingsService.Load().Language);
         base.OnStartup(e);
 
-        // UI 執行緒（含 async void 回拋）的未攔截例外：記 log、提示、標記 Handled 讓程式存活。
-        // 若後續狀態已壞使用者可自行重啟；至少量測結果 / 已載模型不會直接蒸發。
+        // Report UI exceptions and keep the window open.
         DispatcherUnhandledException += (_, args) =>
         {
             LogException("DispatcherUnhandledException", args.Exception);
             MessageBox.Show(
-                $"發生未預期的錯誤，操作已中止（程式將嘗試繼續運作）。\n\n{args.Exception.Message}\n\n" +
-                $"詳細記錄：{LogPath}",
-                "STPViewer 錯誤", MessageBoxButton.OK, MessageBoxImage.Warning);
+                LocalizationService.Format("App.UnexpectedError", args.Exception.Message, LogPath),
+                LocalizationService.Get("App.ErrorTitle"), MessageBoxButton.OK, MessageBoxImage.Warning);
             args.Handled = true;
         };
 
-        // 沒被 await 的背景 Task 例外（finalizer 階段才浮出）：記 log 並標記已觀察，避免行程終止
+        // Log unobserved task exceptions.
         TaskScheduler.UnobservedTaskException += (_, args) =>
         {
             LogException("UnobservedTaskException", args.Exception);
             args.SetObserved();
         };
 
-        // 其他非 UI 執行緒的致命例外：無法阻止終止，但至少留下記錄
+        // Log fatal exceptions on non-UI threads.
         AppDomain.CurrentDomain.UnhandledException += (_, args) =>
             LogException("AppDomainUnhandledException", args.ExceptionObject as Exception);
     }
@@ -55,6 +55,6 @@ public partial class App : Application
             sb.AppendLine(new string('-', 80));
             File.AppendAllText(LogPath, sb.ToString(), Encoding.UTF8);
         }
-        catch { /* logging 本身失敗不能再拋 */ }
+        catch { /* Logging must not throw from an exception handler. */ }
     }
 }
diff --git a/src/STPViewer/Converters/EnumToBoolConverter.cs b/src/STPViewer/Converters/EnumToBoolConverter.cs
index 00e0f06..b830c59 100644
--- a/src/STPViewer/Converters/EnumToBoolConverter.cs
+++ b/src/STPViewer/Converters/EnumToBoolConverter.cs
@@ -6,8 +6,8 @@ using STPViewer.Models;
 namespace STPViewer.Converters;
 
 /// <summary>
-/// MeasureMode ↔ ToggleButton.IsChecked。
-/// ConverterParameter 為模式名稱字串；取消勾選時回到 None。
+/// Convert MeasureMode to ToggleButton.IsChecked using the mode name
+/// in ConverterParameter. Unchecking returns to None.
 /// </summary>
 public class EnumToBoolConverter : IValueConverter
 {
diff --git a/src/STPViewer/Converters/FileNameConverter.cs b/src/STPViewer/Converters/FileNameConverter.cs
index 924ea12..3b0461a 100644
--- a/src/STPViewer/Converters/FileNameConverter.cs
+++ b/src/STPViewer/Converters/FileNameConverter.cs
@@ -4,7 +4,7 @@ using System.Windows.Data;
 
 namespace STPViewer.Converters;
 
-/// <summary>完整路徑 → 檔名（選單「最近檔案」顯示用；tooltip 仍給完整路徑）</summary>
+/// <summary>Show file names in the recent-files menu while retaining full paths as tooltips.</summary>
 public class FileNameConverter : IValueConverter
 {
     public object Convert(object? value, Type targetType, object? parameter, CultureInfo culture) =>
diff --git a/src/STPViewer/Localization/LocExtension.cs b/src/STPViewer/Localization/LocExtension.cs
new file mode 100644
index 0000000..b1608b9
--- /dev/null
+++ b/src/STPViewer/Localization/LocExtension.cs
@@ -0,0 +1,20 @@
+using System.Windows.Data;
+using System.Windows.Markup;
+using STPViewer.Services;
+
+namespace STPViewer.Localization;
+
+[MarkupExtensionReturnType(typeof(string))]
+public class LocExtension : MarkupExtension
+{
+    public string Key { get; set; }
+
+    public LocExtension(string key) => Key = key;
+
+    public override object ProvideValue(IServiceProvider serviceProvider) =>
+        new Binding($"[{Key}]")
+        {
+            Source = LocalizationService.Instance,
+            Mode = BindingMode.OneWay,
+        }.ProvideValue(serviceProvider);
+}
diff --git a/src/STPViewer/MainWindow.xaml b/src/STPViewer/MainWindow.xaml
index 24fb420..4b981b8 100644
--- a/src/STPViewer/MainWindow.xaml
+++ b/src/STPViewer/MainWindow.xaml
@@ -4,7 +4,8 @@
         xmlns:h="http://helix-toolkit.org/wpf"
         xmlns:conv="clr-namespace:STPViewer.Converters"
         xmlns:vm="clr-namespace:STPViewer.ViewModels"
-        Title="STPViewer — STP/STEP 3D 檢視器"
+        xmlns:loc="clr-namespace:STPViewer.Localization"
+        Title="{loc:Loc Ui.Main.WindowTitle}"
         Height="820" Width="1320"
         WindowStartupLocation="CenterScreen"
         AllowDrop="True" Drop="Window_Drop" DragOver="Window_DragOver"
@@ -27,12 +28,12 @@
     </Window.Resources>
 
     <DockPanel>
-        <!-- ─── 選單列（全部功能，分類下拉）─── -->
+        <!-- Menu bar -->
         <Menu DockPanel.Dock="Top">
-            <MenuItem Header="檔案(_F)">
-                <MenuItem Header="📂 匯入…" Command="{Binding ImportCommand}"
-                          ToolTip="匯入 STP/STEP/STL/DXF（可複選，也可直接拖放到視窗）" />
-                <MenuItem Header="最近檔案" ItemsSource="{Binding RecentFiles}">
+            <MenuItem Header="{loc:Loc Ui.Main.FileF}">
+                <MenuItem Header="{loc:Loc Ui.Main.MenuImport}" Command="{Binding ImportCommand}"
+                          ToolTip="{loc:Loc Ui.Main.ImportSTPSTEPSTLDXFFiles}" />
+                <MenuItem Header="{loc:Loc Ui.Main.RecentFiles}" ItemsSource="{Binding RecentFiles}">
                     <MenuItem.ItemContainerStyle>
                         <Style TargetType="MenuItem">
                             <Setter Property="Header" Value="{Binding Converter={StaticResource FileNameConv}}" />
@@ -44,83 +45,96 @@
                     </MenuItem.ItemContainerStyle>
                 </MenuItem>
                 <Separator />
-                <MenuItem Header="💾 匯出量測 CSV…" Command="{Binding ExportCsvCommand}" />
-                <MenuItem Header="📷 視圖截圖 PNG…" Command="{Binding SaveScreenshotCommand}"
-                          ToolTip="3D 視圖截圖存 PNG（2x 解析度）" />
-                <MenuItem Header="📤 匯出 STEP…" Command="{Binding ExportStepFileCommand}"
-                          ToolTip="把可見檔案（目前對齊位置）匯出成新 STEP 檔；不動原始檔" />
-                <MenuItem Header="📐 匯出 STL…" Command="{Binding ExportStlFileCommand}"
-                          ToolTip="先設定範圍/格式/單位/精度，確認再匯出" />
+                <MenuItem Header="{loc:Loc Ui.Main.ExportMeasurementsCSV}" Command="{Binding ExportCsvCommand}" />
+                <MenuItem Header="{loc:Loc Ui.Main.SaveViewPNG}" Command="{Binding SaveScreenshotCommand}"
+                          ToolTip="{loc:Loc Ui.Main.SavePNGScreenshot3DView2}" />
+                <MenuItem Header="{loc:Loc Ui.Main.ExportSTEP}" Command="{Binding ExportStepFileCommand}"
+                          ToolTip="{loc:Loc Ui.Main.ExportStepTooltip}" />
+                <MenuItem Header="{loc:Loc Ui.Main.ExportSTL}" Command="{Binding ExportStlFileCommand}"
+                          ToolTip="{loc:Loc Ui.Main.ChooseScopeFormatUnitsMeshQuality}" />
             </MenuItem>
-            <MenuItem Header="視圖(_V)">
-                <MenuItem Header="🔍 縮放至全部" Command="{Binding ZoomAllCommand}" />
+            <MenuItem Header="{loc:Loc Ui.Main.ViewV}">
+                <MenuItem Header="{loc:Loc Ui.Main.ZoomFit}" Command="{Binding ZoomAllCommand}" />
                 <Separator />
-                <MenuItem Header="等角視圖" Command="{Binding SetStandardViewCommand}" CommandParameter="Iso" />
-                <MenuItem Header="前視圖" Command="{Binding SetStandardViewCommand}" CommandParameter="Front"
-                          ToolTip="-Y 方向看，Z 向上" />
-                <MenuItem Header="上視圖" Command="{Binding SetStandardViewCommand}" CommandParameter="Top"
-                          ToolTip="+Z 往下看" />
-                <MenuItem Header="右視圖" Command="{Binding SetStandardViewCommand}" CommandParameter="Right"
-                          ToolTip="+X 方向看，Z 向上" />
+                <MenuItem Header="{loc:Loc Ui.Main.IsometricView}" Command="{Binding SetStandardViewCommand}" CommandParameter="Iso" />
+                <MenuItem Header="{loc:Loc Ui.Main.FrontView}" Command="{Binding SetStandardViewCommand}" CommandParameter="Front"
+                          ToolTip="{loc:Loc Ui.Main.LookAlongYZUp}" />
+                <MenuItem Header="{loc:Loc Ui.Main.TopView}" Command="{Binding SetStandardViewCommand}" CommandParameter="Top"
+                          ToolTip="{loc:Loc Ui.Main.LookDownFromZ}" />
+                <MenuItem Header="{loc:Loc Ui.Main.RightView}" Command="{Binding SetStandardViewCommand}" CommandParameter="Right"
+                          ToolTip="{loc:Loc Ui.Main.LookAlongXZUp}" />
                 <Separator />
-                <MenuItem Header="正交投影" IsCheckable="True" IsChecked="{Binding OrthographicView}"
-                          ToolTip="平行投影，量尺寸不受透視變形；取消勾選切回透視" />
-                <MenuItem Header="單位顯示 inch（mm ⇄ in）" IsCheckable="True" IsChecked="{Binding UseInch}"
-                          ToolTip="既有量測即時換算；內部一律存 mm" />
+                <MenuItem Header="{loc:Loc Ui.Main.OrthographicProjection}" IsCheckable="True" IsChecked="{Binding OrthographicView}"
+                          ToolTip="{loc:Loc Ui.Main.ParallelProjectionAvoidsPerspectiveDistortionUncheck}" />
+                <MenuItem Header="{loc:Loc Ui.Main.DisplayInchesMm}" IsCheckable="True" IsChecked="{Binding UseInch}"
+                          ToolTip="{loc:Loc Ui.Main.ExistingMeasurementsUpdateImmediatelyValuesStored}" />
+                <Separator />
+                <MenuItem Header="{loc:Loc Ui.Language}" ItemsSource="{Binding Languages}">
+                    <MenuItem.ItemContainerStyle>
+                        <Style TargetType="MenuItem">
+                            <Setter Property="Header" Value="{Binding Key}" />
+                            <Setter Property="IsCheckable" Value="True" />
+                            <Setter Property="IsChecked" Value="{Binding IsSelected, Mode=OneWay}" />
+                            <Setter Property="Command"
+                                    Value="{Binding DataContext.ChangeLanguageCommand, RelativeSource={RelativeSource AncestorType=Menu}}" />
+                            <Setter Property="CommandParameter" Value="{Binding Id}" />
+                        </Style>
+                    </MenuItem.ItemContainerStyle>
+                </MenuItem>
             </MenuItem>
-            <MenuItem Header="量測(_M)">
-                <MenuItem Header="📍 點座標" IsCheckable="True" InputGestureText="P"
+            <MenuItem Header="{loc:Loc Ui.Main.MeasureM}">
+                <MenuItem Header="{loc:Loc Ui.Main.PointCoordinates}" IsCheckable="True" InputGestureText="P"
                           IsChecked="{Binding CurrentMode, Converter={StaticResource ModeConv}, ConverterParameter=Point}"
-                          ToolTip="量測點座標（吸附頂點/圓心）" />
-                <MenuItem Header="📏 兩點距離" IsCheckable="True" InputGestureText="D"
+                          ToolTip="{loc:Loc Ui.Main.MeasurePointCoordinatesSnapsVerticesCircle}" />
+                <MenuItem Header="{loc:Loc Ui.Main.TwoPointDistance}" IsCheckable="True" InputGestureText="D"
                           IsChecked="{Binding CurrentMode, Converter={StaticResource ModeConv}, ConverterParameter=Distance}"
-                          ToolTip="兩點距離 + ΔXYZ（點到圓邊會吸圓心 → 可量孔對孔 pitch）" />
-                <MenuItem Header="📐 邊長" IsCheckable="True" InputGestureText="E"
+                          ToolTip="{loc:Loc Ui.Main.DistanceXYZCircularEdgesSnapCenters}" />
+                <MenuItem Header="{loc:Loc Ui.Main.EdgeLength}" IsCheckable="True" InputGestureText="E"
                           IsChecked="{Binding CurrentMode, Converter={StaticResource ModeConv}, ConverterParameter=Edge}"
-                          ToolTip="邊長（直線/曲線/圓弧）" />
-                <MenuItem Header="⬛ 面" IsCheckable="True" InputGestureText="F"
+                          ToolTip="{loc:Loc Ui.Main.MeasureStraightCurvedCircularEdgeLengths}" />
+                <MenuItem Header="{loc:Loc Ui.Main.Face}" IsCheckable="True" InputGestureText="F"
                           IsChecked="{Binding CurrentMode, Converter={StaticResource ModeConv}, ConverterParameter=Face}"
-                          ToolTip="面積 + 曲面類型/法向量" />
-                <MenuItem Header="⭕ 圓" IsCheckable="True" InputGestureText="C"
+                          ToolTip="{loc:Loc Ui.Main.AreaSurfaceTypeNormalVector}" />
+                <MenuItem Header="{loc:Loc Ui.Main.Circle}" IsCheckable="True" InputGestureText="C"
                           IsChecked="{Binding CurrentMode, Converter={StaticResource ModeConv}, ConverterParameter=Circle}"
-                          ToolTip="圓心/半徑/直徑/周長" />
-                <MenuItem Header="∠ 角度" IsCheckable="True" InputGestureText="A"
+                          ToolTip="{loc:Loc Ui.Main.CenterRadiusDiameterCircumference}" />
+                <MenuItem Header="{loc:Loc Ui.Main.Angle}" IsCheckable="True" InputGestureText="A"
                           IsChecked="{Binding CurrentMode, Converter={StaticResource ModeConv}, ConverterParameter=Angle}"
-                          ToolTip="兩面/兩邊夾角（點兩個面或靠近直線邊）" />
-                <MenuItem Header="⇔ 面距" IsCheckable="True" InputGestureText="M"
+                          ToolTip="{loc:Loc Ui.Main.AngleBetweenTwoFacesStraightEdges}" />
+                <MenuItem Header="{loc:Loc Ui.Main.FaceDistance}" IsCheckable="True" InputGestureText="M"
                           IsChecked="{Binding CurrentMode, Converter={StaticResource ModeConv}, ConverterParameter=FaceDistance}"
-                          ToolTip="面到面最短距離（網格近似）" />
+                          ToolTip="{loc:Loc Ui.Main.ShortestDistanceBetweenFacesMeshApproximation}" />
                 <Separator />
-                <MenuItem Header="🧹 清除全部量測" Command="{Binding ClearMeasurementsCommand}"
-                          InputGestureText="Esc" ToolTip="Esc = 取消進行中量測/退出模式" />
+                <MenuItem Header="{loc:Loc Ui.Main.ClearAllMeasurements}" Command="{Binding ClearMeasurementsCommand}"
+                          InputGestureText="Esc" ToolTip="{loc:Loc Ui.Main.EscCancelsCurrentMeasurementExitsMode}" />
             </MenuItem>
-            <MenuItem Header="變換(_T)">
-                <MenuItem Header="🎯 兩點對齊（平移）" IsCheckable="True"
+            <MenuItem Header="{loc:Loc Ui.Main.TransformT}">
+                <MenuItem Header="{loc:Loc Ui.Main.TwoPointAlignmentTranslate}" IsCheckable="True"
                           IsChecked="{Binding CurrentMode, Converter={StaticResource ModeConv}, ConverterParameter=Align}"
-                          ToolTip="先點要移動零件上的點，再點目標點" />
-                <MenuItem Header="🎯 三點對齊（旋轉+平移）" IsCheckable="True"
+                          ToolTip="{loc:Loc Ui.Main.PickPointPartMoveThenPick}" />
+                <MenuItem Header="{loc:Loc Ui.Main.ThreePointAlignmentRotateTranslate}" IsCheckable="True"
                           IsChecked="{Binding CurrentMode, Converter={StaticResource ModeConv}, ConverterParameter=Align3}"
-                          ToolTip="先在要移動的檔案點 3 個特徵點，再到目標檔案點 3 個對應點（順序對應）" />
-                <MenuItem Header="🖐 拖曳模式" IsCheckable="True"
+                          ToolTip="{loc:Loc Ui.Main.PickThreePointsMovingModelThen}" />
+                <MenuItem Header="{loc:Loc Ui.Main.DragMode}" IsCheckable="True"
                           IsChecked="{Binding CurrentMode, Converter={StaticResource ModeConv}, ConverterParameter=Drag}"
-                          ToolTip="左鍵按住零件沿螢幕平面拖動，放開定位" />
-                <MenuItem Header="⊹ 三軸操作器" IsCheckable="True" IsChecked="{Binding GizmoEnabled}"
-                          ToolTip="對樹面板選取的檔案顯示 XYZ 箭頭與旋轉環，每次放開即定位" />
+                          ToolTip="{loc:Loc Ui.Main.HoldLeftMouseButtonMovePart}" />
+                <MenuItem Header="{loc:Loc Ui.Main.3AxisGizmo}" IsCheckable="True" IsChecked="{Binding GizmoEnabled}"
+                          ToolTip="{loc:Loc Ui.Main.ShowXYZArrowsRotationRingsSelected}" />
                 <Separator />
-                <MenuItem Header="↻ 繞 X 軸 +90°" Command="{Binding RotateRootCommand}" CommandParameter="X"
-                          ToolTip="對樹面板選取的檔案，繞其中心旋轉（先在樹面板點選檔案）" />
-                <MenuItem Header="↻ 繞 Y 軸 +90°" Command="{Binding RotateRootCommand}" CommandParameter="Y" />
-                <MenuItem Header="↻ 繞 Z 軸 +90°" Command="{Binding RotateRootCommand}" CommandParameter="Z" />
+                <MenuItem Header="{loc:Loc Ui.Main.Rotate90AroundX}" Command="{Binding RotateRootCommand}" CommandParameter="X"
+                          ToolTip="{loc:Loc Ui.Main.RotateModelSelectedTreeAroundIts}" />
+                <MenuItem Header="{loc:Loc Ui.Main.Rotate90AroundY}" Command="{Binding RotateRootCommand}" CommandParameter="Y" />
+                <MenuItem Header="{loc:Loc Ui.Main.Rotate90AroundZ}" Command="{Binding RotateRootCommand}" CommandParameter="Z" />
             </MenuItem>
-            <MenuItem Header="工具(_L)">
-                <MenuItem Header="🧩 干涉檢查" Command="{Binding CheckInterferenceCommand}"
-                          ToolTip="2 個以上可見檔案兩兩檢查是否相交；無相交時回報最小間隙" />
-                <MenuItem Header="✂ 剖面檢視" IsCheckable="True" IsChecked="{Binding SectionEnabled}"
-                          ToolTip="開啟後下方出現剖面參數列（軸向/位置/反向）" />
+            <MenuItem Header="{loc:Loc Ui.Main.ToolsL}">
+                <MenuItem Header="{loc:Loc Ui.Main.InterferenceCheck}" Command="{Binding CheckInterferenceCommand}"
+                          ToolTip="{loc:Loc Ui.Main.CheckVisibleModelPairsIntersectionsReport}" />
+                <MenuItem Header="{loc:Loc Ui.Main.SectionView}" IsCheckable="True" IsChecked="{Binding SectionEnabled}"
+                          ToolTip="{loc:Loc Ui.Main.ShowSectionControlsAxisPositionDirection}" />
             </MenuItem>
-            <MenuItem Header="快速列(_Q)">
-                <MenuItem Header="自訂按鈕" ItemsSource="{Binding QuickBar.Items}"
-                          ToolTip="勾選要顯示在快速列的常用按鈕（隨設定保存）">
+            <MenuItem Header="{loc:Loc Ui.Main.QuickBarQ}">
+                <MenuItem Header="{loc:Loc Ui.Main.CustomizeButtons}" ItemsSource="{Binding QuickBar.Items}"
+                          ToolTip="{loc:Loc Ui.Main.CheckButtonsShowQuickBarSaved}">
                     <MenuItem.ItemContainerStyle>
                         <Style TargetType="MenuItem">
                             <Setter Property="Header" Value="{Binding Label}" />
@@ -131,138 +145,142 @@
                     </MenuItem.ItemContainerStyle>
                 </MenuItem>
                 <Separator />
-                <MenuItem Header="恢復預設按鈕" Command="{Binding QuickBar.ResetDefaultsCommand}" />
+                <MenuItem Header="{loc:Loc Ui.Main.RestoreDefaultButtons}" Command="{Binding QuickBar.ResetDefaultsCommand}" />
             </MenuItem>
-            <MenuItem Header="說明(_H)">
-                <MenuItem Header="ℹ 關於 STPViewer…" Click="About_Click"
-                          ToolTip="程式資訊與版本紀錄" />
+            <MenuItem Header="{loc:Loc Ui.Main.HelpH}">
+                <MenuItem Header="{loc:Loc Ui.Main.IAboutSTPViewer}" Click="About_Click"
+                          ToolTip="{loc:Loc Ui.Main.ApplicationInformationReleaseHistory}" />
             </MenuItem>
         </Menu>
 
-        <!-- ─── 快速工具列（可自訂：選單「快速列 → 自訂按鈕」勾選）─── -->
+        <!-- Customizable Quick Bar -->
         <ToolBarTray DockPanel.Dock="Top">
             <ToolBar>
                 <Button Style="{StaticResource QuickButton}" Command="{Binding ImportCommand}"
                         Visibility="{Binding QuickBar[Import].IsChecked, Converter={StaticResource BoolToVis}}"
-                        ToolTip="匯入 STP/STEP/STL/DXF（可複選，也可直接拖放到視窗）">📂 匯入</Button>
+                        ToolTip="{loc:Loc Ui.Main.ImportSTPSTEPSTLDXFFiles}" Content="{loc:Loc Ui.Main.ToolbarImport}" />
                 <Button Style="{StaticResource QuickButton}" Click="Recent_Click" Padding="4,4"
                         Visibility="{Binding QuickBar[Recent].IsChecked, Converter={StaticResource BoolToVis}}"
-                        ToolTip="最近開啟的檔案">▾</Button>
+                        ToolTip="{loc:Loc Ui.Main.RecentlyOpenedFiles}">▾</Button>
                 <Button Style="{StaticResource QuickButton}" Command="{Binding ZoomAllCommand}"
                         Visibility="{Binding QuickBar[ZoomAll].IsChecked, Converter={StaticResource BoolToVis}}"
-                        ToolTip="縮放至全部模型">🔍 全覽</Button>
+                        ToolTip="{loc:Loc Ui.Main.FitAllModelsView}" Content="{loc:Loc Ui.Main.Fit}" />
                 <Button Style="{StaticResource QuickButton}" Command="{Binding SetStandardViewCommand}" CommandParameter="Iso"
                         Visibility="{Binding QuickBar[ViewIso].IsChecked, Converter={StaticResource BoolToVis}}"
-                        ToolTip="等角視圖">等角</Button>
+                        ToolTip="{loc:Loc Ui.Main.IsometricView}" Content="{loc:Loc Ui.Main.Iso}" />
                 <Button Style="{StaticResource QuickButton}" Command="{Binding SetStandardViewCommand}" CommandParameter="Front"
                         Visibility="{Binding QuickBar[ViewFront].IsChecked, Converter={StaticResource BoolToVis}}"
-                        ToolTip="前視圖（-Y 方向看，Z 向上）">前</Button>
+                        ToolTip="{loc:Loc Ui.Main.FrontViewLookAlongYZ}" Content="{loc:Loc Ui.Main.Front}" />
                 <Button Style="{StaticResource QuickButton}" Command="{Binding SetStandardViewCommand}" CommandParameter="Top"
                         Visibility="{Binding QuickBar[ViewTop].IsChecked, Converter={StaticResource BoolToVis}}"
-                        ToolTip="上視圖（+Z 往下看）">上</Button>
+                        ToolTip="{loc:Loc Ui.Main.TopViewLookDownFromZ}" Content="{loc:Loc Ui.Main.Top}" />
                 <Button Style="{StaticResource QuickButton}" Command="{Binding SetStandardViewCommand}" CommandParameter="Right"
                         Visibility="{Binding QuickBar[ViewRight].IsChecked, Converter={StaticResource BoolToVis}}"
-                        ToolTip="右視圖（+X 方向看，Z 向上）">右</Button>
+                        ToolTip="{loc:Loc Ui.Main.RightViewLookAlongXZ}" Content="{loc:Loc Ui.Main.Right}" />
                 <ToggleButton Style="{StaticResource ModeButton}" IsChecked="{Binding OrthographicView}"
                               Visibility="{Binding QuickBar[Ortho].IsChecked, Converter={StaticResource BoolToVis}}"
-                              ToolTip="正交投影（平行投影，量尺寸不受透視變形；再按切回透視）">正交</ToggleButton>
-                <ToggleButton Style="{StaticResource ModeButton}" ToolTip="量測點座標（吸附頂點/圓心）— 快速鍵 P"
+                              ToolTip="{loc:Loc Ui.Main.OrthographicProjectionAvoidsPerspectiveDistortionClick}" Content="{loc:Loc Ui.Main.Ortho}" />
+                <ToggleButton Style="{StaticResource ModeButton}" ToolTip="{loc:Loc Ui.Main.PointCoordinatesVertexCircleCenterSnapping}"
                               Visibility="{Binding QuickBar[Point].IsChecked, Converter={StaticResource BoolToVis}}"
-                              IsChecked="{Binding CurrentMode, Converter={StaticResource ModeConv}, ConverterParameter=Point}">📍 點</ToggleButton>
-                <ToggleButton Style="{StaticResource ModeButton}" ToolTip="兩點距離 + ΔXYZ（點到圓邊會吸圓心 → 可量孔對孔 pitch）— 快速鍵 D"
+                              IsChecked="{Binding CurrentMode, Converter={StaticResource ModeConv}, ConverterParameter=Point}" Content="{loc:Loc Ui.Main.Point}" />
+                <ToggleButton Style="{StaticResource ModeButton}" ToolTip="{loc:Loc Ui.Main.DistanceXYZCircleCenterSnappingHole}"
                               Visibility="{Binding QuickBar[Distance].IsChecked, Converter={StaticResource BoolToVis}}"
-                              IsChecked="{Binding CurrentMode, Converter={StaticResource ModeConv}, ConverterParameter=Distance}">📏 距離</ToggleButton>
-                <ToggleButton Style="{StaticResource ModeButton}" ToolTip="邊長（直線/曲線/圓弧）— 快速鍵 E"
+                              IsChecked="{Binding CurrentMode, Converter={StaticResource ModeConv}, ConverterParameter=Distance}" Content="{loc:Loc Ui.Main.Distance}" />
+                <ToggleButton Style="{StaticResource ModeButton}" ToolTip="{loc:Loc Ui.Main.StraightCurvedCircularEdgeLengthShortcut}"
                               Visibility="{Binding QuickBar[Edge].IsChecked, Converter={StaticResource BoolToVis}}"
-                              IsChecked="{Binding CurrentMode, Converter={StaticResource ModeConv}, ConverterParameter=Edge}">📐 邊</ToggleButton>
-                <ToggleButton Style="{StaticResource ModeButton}" ToolTip="面積 + 曲面類型/法向量 — 快速鍵 F"
+                              IsChecked="{Binding CurrentMode, Converter={StaticResource ModeConv}, ConverterParameter=Edge}" Content="{loc:Loc Ui.Main.Edge}" />
+                <ToggleButton Style="{StaticResource ModeButton}" ToolTip="{loc:Loc Ui.Main.AreaSurfaceTypeNormalVectorShortcut}"
                               Visibility="{Binding QuickBar[Face].IsChecked, Converter={StaticResource BoolToVis}}"
-                              IsChecked="{Binding CurrentMode, Converter={StaticResource ModeConv}, ConverterParameter=Face}">⬛ 面</ToggleButton>
-                <ToggleButton Style="{StaticResource ModeButton}" ToolTip="圓心/半徑/直徑/周長 — 快速鍵 C"
+                              IsChecked="{Binding CurrentMode, Converter={StaticResource ModeConv}, ConverterParameter=Face}" Content="{loc:Loc Ui.Main.Face}" />
+                <ToggleButton Style="{StaticResource ModeButton}" ToolTip="{loc:Loc Ui.Main.CenterRadiusDiameterCircumferenceShortcutC}"
                               Visibility="{Binding QuickBar[Circle].IsChecked, Converter={StaticResource BoolToVis}}"
-                              IsChecked="{Binding CurrentMode, Converter={StaticResource ModeConv}, ConverterParameter=Circle}">⭕ 圓</ToggleButton>
-                <ToggleButton Style="{StaticResource ModeButton}" ToolTip="兩面/兩邊夾角（點兩個面或靠近直線邊）— 快速鍵 A"
+                              IsChecked="{Binding CurrentMode, Converter={StaticResource ModeConv}, ConverterParameter=Circle}" Content="{loc:Loc Ui.Main.Circle}" />
+                <ToggleButton Style="{StaticResource ModeButton}" ToolTip="{loc:Loc Ui.Main.AngleBetweenFacesStraightEdgesShortcut}"
                               Visibility="{Binding QuickBar[Angle].IsChecked, Converter={StaticResource BoolToVis}}"
-                              IsChecked="{Binding CurrentMode, Converter={StaticResource ModeConv}, ConverterParameter=Angle}">∠ 角度</ToggleButton>
-                <ToggleButton Style="{StaticResource ModeButton}" ToolTip="面到面最短距離（網格近似）— 快速鍵 M"
+                              IsChecked="{Binding CurrentMode, Converter={StaticResource ModeConv}, ConverterParameter=Angle}" Content="{loc:Loc Ui.Main.Angle}" />
+                <ToggleButton Style="{StaticResource ModeButton}" ToolTip="{loc:Loc Ui.Main.ShortestFaceDistanceMeshApproximationShortcut}"
                               Visibility="{Binding QuickBar[FaceDistance].IsChecked, Converter={StaticResource BoolToVis}}"
-                              IsChecked="{Binding CurrentMode, Converter={StaticResource ModeConv}, ConverterParameter=FaceDistance}">⇔ 面距</ToggleButton>
+                              IsChecked="{Binding CurrentMode, Converter={StaticResource ModeConv}, ConverterParameter=FaceDistance}" Content="{loc:Loc Ui.Main.FaceDistance}" />
                 <ToggleButton Style="{StaticResource ModeButton}"
-                              ToolTip="兩點對齊（平移零件）：先點要移動零件上的點，再點目標點"
+                              ToolTip="{loc:Loc Ui.Main.TwoPointAlignmentPickPointMoving}"
                               Visibility="{Binding QuickBar[Align].IsChecked, Converter={StaticResource BoolToVis}}"
-                              IsChecked="{Binding CurrentMode, Converter={StaticResource ModeConv}, ConverterParameter=Align}">🎯 對齊</ToggleButton>
+                              IsChecked="{Binding CurrentMode, Converter={StaticResource ModeConv}, ConverterParameter=Align}" Content="{loc:Loc Ui.Main.Align}" />
                 <ToggleButton Style="{StaticResource ModeButton}"
-                              ToolTip="三點對齊（旋轉+平移）：先在要移動的檔案點 3 個特徵點，再到目標檔案點 3 個對應點（順序對應）"
+                              ToolTip="{loc:Loc Ui.Main.ThreePointAlignmentPickThreePoints}"
                               Visibility="{Binding QuickBar[Align3].IsChecked, Converter={StaticResource BoolToVis}}"
-                              IsChecked="{Binding CurrentMode, Converter={StaticResource ModeConv}, ConverterParameter=Align3}">🎯 三點</ToggleButton>
+                              IsChecked="{Binding CurrentMode, Converter={StaticResource ModeConv}, ConverterParameter=Align3}" Content="{loc:Loc Ui.Main.3Point}" />
                 <Button Style="{StaticResource QuickButton}" Command="{Binding RotateRootCommand}" CommandParameter="X"
                         Visibility="{Binding QuickBar[RotateX].IsChecked, Converter={StaticResource BoolToVis}}"
-                        ToolTip="選取的檔案繞 X 軸 +90°（先在樹面板點選檔案）">↻X</Button>
+                        ToolTip="{loc:Loc Ui.Main.RotateModelSelectedTree90Around}">↻X</Button>
                 <Button Style="{StaticResource QuickButton}" Command="{Binding RotateRootCommand}" CommandParameter="Y"
                         Visibility="{Binding QuickBar[RotateY].IsChecked, Converter={StaticResource BoolToVis}}"
-                        ToolTip="選取的檔案繞 Y 軸 +90°">↻Y</Button>
+                        ToolTip="{loc:Loc Ui.Main.RotateSelectedModel90AroundY}">↻Y</Button>
                 <Button Style="{StaticResource QuickButton}" Command="{Binding RotateRootCommand}" CommandParameter="Z"
                         Visibility="{Binding QuickBar[RotateZ].IsChecked, Converter={StaticResource BoolToVis}}"
-                        ToolTip="選取的檔案繞 Z 軸 +90°">↻Z</Button>
+                        ToolTip="{loc:Loc Ui.Main.RotateSelectedModel90AroundZ}">↻Z</Button>
                 <ToggleButton Style="{StaticResource ModeButton}"
-                              ToolTip="拖曳模式：左鍵按住零件沿螢幕平面拖動，放開定位（深度方向先轉視角再拖）"
+                              ToolTip="{loc:Loc Ui.Main.DragModeHoldLeftMouseButton}"
                               Visibility="{Binding QuickBar[Drag].IsChecked, Converter={StaticResource BoolToVis}}"
-                              IsChecked="{Binding CurrentMode, Converter={StaticResource ModeConv}, ConverterParameter=Drag}">🖐 拖曳</ToggleButton>
+                              IsChecked="{Binding CurrentMode, Converter={StaticResource ModeConv}, ConverterParameter=Drag}" Content="{loc:Loc Ui.Main.Drag}" />
                 <ToggleButton Style="{StaticResource ModeButton}" IsChecked="{Binding GizmoEnabled}"
                               Visibility="{Binding QuickBar[Gizmo].IsChecked, Converter={StaticResource BoolToVis}}"
-                              ToolTip="三軸操作器：對樹面板選取的檔案顯示 XYZ 箭頭（沿軸移動）與旋轉環（繞軸轉任意角度），每次放開即定位">⊹ 操作器</ToggleButton>
+                              ToolTip="{loc:Loc Ui.Main.3AxisGizmoUseXYZArrows}" Content="{loc:Loc Ui.Main.Gizmo}" />
                 <Button Style="{StaticResource QuickButton}" Command="{Binding CheckInterferenceCommand}"
                         Visibility="{Binding QuickBar[Interference].IsChecked, Converter={StaticResource BoolToVis}}"
-                        ToolTip="干涉檢查：2 個以上可見檔案兩兩檢查是否相交（match 判定）；無相交時回報最小間隙">🧩 干涉</Button>
+                        ToolTip="{loc:Loc Ui.Main.InterferenceCheckTestVisibleModelPairs}" Content="{loc:Loc Ui.Main.Interference}" />
                 <ToggleButton Style="{StaticResource ModeButton}" IsChecked="{Binding SectionEnabled}"
                               Visibility="{Binding QuickBar[Section].IsChecked, Converter={StaticResource BoolToVis}}"
-                              ToolTip="開啟/關閉剖面檢視（開啟後下方出現參數列）">✂ 剖面</ToggleButton>
+                              ToolTip="{loc:Loc Ui.Main.ToggleSectionViewItsControls}" Content="{loc:Loc Ui.Main.ToolbarSection}" />
                 <Button Style="{StaticResource QuickButton}" Command="{Binding ClearMeasurementsCommand}"
                         Visibility="{Binding QuickBar[Clear].IsChecked, Converter={StaticResource BoolToVis}}"
-                        ToolTip="清除全部量測與標記（Esc = 取消進行中量測/退出模式）">🧹 清除</Button>
+                        ToolTip="{loc:Loc Ui.Main.ClearAllMeasurementsMarkersEscCancels}" Content="{loc:Loc Ui.Main.Clear}" />
                 <ToggleButton Style="{StaticResource ModeButton}" IsChecked="{Binding UseInch}"
                               Visibility="{Binding QuickBar[Unit].IsChecked, Converter={StaticResource BoolToVis}}"
-                              ToolTip="切換顯示單位 mm ⇄ inch（既有量測即時換算）">mm ⇄ in</ToggleButton>
+                              ToolTip="{loc:Loc Ui.Main.SwitchDisplayUnitsBetweenMmInches}">mm ⇄ in</ToggleButton>
                 <Button Style="{StaticResource QuickButton}" Command="{Binding ExportCsvCommand}"
                         Visibility="{Binding QuickBar[ExportCsv].IsChecked, Converter={StaticResource BoolToVis}}"
-                        ToolTip="量測結果匯出 CSV">💾 CSV</Button>
+                        ToolTip="{loc:Loc Ui.Main.ExportMeasurementResultsCSV}">💾 CSV</Button>
                 <Button Style="{StaticResource QuickButton}" Command="{Binding SaveScreenshotCommand}"
                         Visibility="{Binding QuickBar[Screenshot].IsChecked, Converter={StaticResource BoolToVis}}"
-                        ToolTip="3D 視圖截圖存 PNG（2x 解析度）">📷 截圖</Button>
+                        ToolTip="{loc:Loc Ui.Main.SavePNGScreenshot3DView2}" Content="{loc:Loc Ui.Main.Capture}" />
                 <Button Style="{StaticResource QuickButton}" Command="{Binding ExportStepFileCommand}"
                         Visibility="{Binding QuickBar[ExportStep].IsChecked, Converter={StaticResource BoolToVis}}"
-                        ToolTip="把可見檔案（目前對齊位置）匯出成新 STEP 檔 — 對齊插合結果可交接 CAD；不動原始檔">📤 STEP</Button>
+                        ToolTip="{loc:Loc Ui.Main.ToolbarExportStepTooltip}">📤 STEP</Button>
                 <Button Style="{StaticResource QuickButton}" Command="{Binding ExportStlFileCommand}"
                         Visibility="{Binding QuickBar[ExportStl].IsChecked, Converter={StaticResource BoolToVis}}"
-                        ToolTip="把可見檔案（目前位置）匯出成 STL 網格檔 — 先設定範圍/格式/單位/精度，確認再匯出">📐 STL</Button>
+                        ToolTip="{loc:Loc Ui.Main.ToolbarExportStlTooltip}">📐 STL</Button>
+                <ComboBox ItemsSource="{Binding Languages}" DisplayMemberPath="Key"
+                          SelectedValue="{Binding SelectedLanguage}" SelectedValuePath="Id"
+                          Visibility="{Binding QuickBar[Language].IsChecked, Converter={StaticResource BoolToVis}}"
+                          ToolTip="{loc:Loc Ui.Language}" Margin="2,0" />
             </ToolBar>
         </ToolBarTray>
 
-        <!-- ─── 剖面參數列（只在剖面開啟時出現）─── -->
+        <!-- Section controls -->
         <ToolBarTray DockPanel.Dock="Top"
                      Visibility="{Binding SectionEnabled, Converter={StaticResource BoolToVis}}">
             <ToolBar>
-                <TextBlock Text="✂ 剖面：" VerticalAlignment="Center" Margin="4,0,2,0" />
+                <TextBlock Text="{loc:Loc Ui.Main.SectionLabel}" VerticalAlignment="Center" Margin="4,0,2,0" />
                 <ComboBox SelectedIndex="{Binding SectionAxisIndex}" Width="60" Margin="4,0"
-                          VerticalAlignment="Center" ToolTip="剖切軸向（3點 = 在模型上點 3 點定義任意平面）">
+                          VerticalAlignment="Center" ToolTip="{loc:Loc Ui.Main.SectionAxis3PointsDefineAn}">
                     <ComboBoxItem>X</ComboBoxItem>
                     <ComboBoxItem>Y</ComboBoxItem>
                     <ComboBoxItem>Z</ComboBoxItem>
-                    <ComboBoxItem>3點</ComboBoxItem>
+                    <ComboBoxItem Content="{loc:Loc Ui.Main.3Points}" />
                 </ComboBox>
                 <Slider Value="{Binding SectionPosition}" Minimum="0" Maximum="100" Width="180"
-                        VerticalAlignment="Center" Margin="4,0" ToolTip="剖面位置（沿法向 %）" />
+                        VerticalAlignment="Center" Margin="4,0" ToolTip="{loc:Loc Ui.Main.SectionPositionAlongNormal}" />
                 <TextBox Text="{Binding SectionPosition, StringFormat={}{0:F0}}" Width="34"
-                         VerticalAlignment="Center" ToolTip="剖面位置 %（0–100，可直接輸入，離開欄位生效）" />
+                         VerticalAlignment="Center" ToolTip="{loc:Loc Ui.Main.SectionPosition0100EnterValue}" />
                 <TextBlock Text="%" VerticalAlignment="Center" Margin="1,0,0,0" />
-                <CheckBox IsChecked="{Binding SectionFlip}" Content="反向" VerticalAlignment="Center"
-                          Margin="4,0" ToolTip="切換保留側" />
+                <CheckBox IsChecked="{Binding SectionFlip}" Content="{loc:Loc Ui.Main.Flip}" VerticalAlignment="Center"
+                          Margin="4,0" ToolTip="{loc:Loc Ui.Main.SwitchRetainedSide}" />
                 <Button Style="{StaticResource QuickButton}" Command="{Binding CloseSectionCommand}"
-                        ToolTip="關閉剖面檢視">✕ 關閉</Button>
+                        ToolTip="{loc:Loc Ui.Main.CloseSectionView}" Content="{loc:Loc Ui.Main.Close}" />
             </ToolBar>
         </ToolBarTray>
 
-        <!-- ─── 狀態列 ─── -->
+        <!-- Status bar -->
         <StatusBar DockPanel.Dock="Bottom">
             <StatusBarItem>
                 <TextBlock Text="{Binding StatusText}" />
@@ -282,12 +300,12 @@
                 <ColumnDefinition Width="300" MinWidth="160" />
             </Grid.ColumnDefinitions>
 
-            <!-- ─── 裝配樹面板 ─── -->
-            <GroupBox Grid.Column="0" Header="模型 / 裝配樹" Margin="4">
+            <!-- Assembly tree -->
+            <GroupBox Grid.Column="0" Header="{loc:Loc Ui.Main.ModelsAssemblyTree}" Margin="4">
                 <DockPanel>
                     <TextBox DockPanel.Dock="Top" Margin="0,2,0,4"
                              Text="{Binding TreeFilter, UpdateSourceTrigger=PropertyChanged}"
-                             ToolTip="輸入名稱過濾裝配樹（只影響樹面板顯示，不影響 3D 可見性；清空 = 全顯）" />
+                             ToolTip="{loc:Loc Ui.Main.FilterAssemblyTreeByNameDoes}" />
                     <TreeView ItemsSource="{Binding Roots}"
                               ScrollViewer.HorizontalScrollBarVisibility="Disabled"
                               VirtualizingPanel.IsVirtualizing="True"
@@ -308,23 +326,23 @@
                                             Tag="{Binding DataContext, RelativeSource={RelativeSource AncestorType=Window}}">
                                     <StackPanel.ContextMenu>
                                         <ContextMenu>
-                                            <MenuItem Header="👁 只顯示此節點"
+                                            <MenuItem Header="{loc:Loc Ui.Main.ShowOnlyThisNode}"
                                                       Command="{Binding PlacementTarget.Tag.IsolateNodeCommand, RelativeSource={RelativeSource AncestorType=ContextMenu}}"
                                                       CommandParameter="{Binding}" />
-                                            <MenuItem Header="🔄 反轉顯示"
+                                            <MenuItem Header="{loc:Loc Ui.Main.InvertVisibility}"
                                                       Command="{Binding PlacementTarget.Tag.InvertVisibilityCommand, RelativeSource={RelativeSource AncestorType=ContextMenu}}" />
-                                            <MenuItem Header="☀ 全部顯示"
+                                            <MenuItem Header="{loc:Loc Ui.Main.ShowAll}"
                                                       Command="{Binding PlacementTarget.Tag.ShowAllCommand, RelativeSource={RelativeSource AncestorType=ContextMenu}}" />
                                             <Separator />
-                                            <MenuItem Header="⚖ 量體積 / 質心"
+                                            <MenuItem Header="{loc:Loc Ui.Main.MeasureVolumeCentroid}"
                                                       Command="{Binding PlacementTarget.Tag.MeasureVolumeCommand, RelativeSource={RelativeSource AncestorType=ContextMenu}}"
                                                       CommandParameter="{Binding}" />
                                         </ContextMenu>
                                     </StackPanel.ContextMenu>
                                     <CheckBox IsChecked="{Binding IsVisible}" VerticalAlignment="Center"
-                                              ToolTip="顯示 / 隱藏（含子節點）" />
+                                              ToolTip="{loc:Loc Ui.Main.ShowHideIncludingChildNodes}" />
                                     <Button Width="14" Height="14" Margin="3,0"
-                                            VerticalAlignment="Center" ToolTip="點擊換色（含子節點）"
+                                            VerticalAlignment="Center" ToolTip="{loc:Loc Ui.Main.ClickChangeColorIncludingChildNodes}"
                                             Command="{Binding CycleColorCommand}">
                                         <Button.Template>
                                             <ControlTemplate TargetType="Button">
@@ -348,16 +366,16 @@
                                             </Style>
                                         </TextBlock.Style>
                                     </TextBlock>
-                                    <CheckBox IsChecked="{Binding ShowEdges}" Content="邊" FontSize="10"
+                                    <CheckBox IsChecked="{Binding ShowEdges}" Content="{loc:Loc Ui.Main.Edges}" FontSize="10"
                                               VerticalAlignment="Center" Margin="4,0,0,0"
                                               Visibility="{Binding IsRoot, Converter={StaticResource BoolToVis}}"
-                                              ToolTip="顯示輪廓邊線（邊線量大時轉動視角會變慢）" />
+                                              ToolTip="{loc:Loc Ui.Main.ShowOutlineEdgesManyEdgesCan}" />
                                     <Button Content="🔍" Width="20" Margin="3,0,0,0" Padding="0"
-                                            VerticalAlignment="Center" ToolTip="縮放至此節點"
+                                            VerticalAlignment="Center" ToolTip="{loc:Loc Ui.Main.ZoomThisNode}"
                                             Command="{Binding DataContext.ZoomNodeCommand, RelativeSource={RelativeSource AncestorType=Window}}"
                                             CommandParameter="{Binding}" />
                                     <Button Content="✕" Width="20" Padding="0" Margin="2,0,0,0"
-                                            VerticalAlignment="Center" ToolTip="移除此檔案"
+                                            VerticalAlignment="Center" ToolTip="{loc:Loc Ui.Main.RemoveThisFile}"
                                             Visibility="{Binding IsRoot, Converter={StaticResource BoolToVis}}"
                                             Command="{Binding DataContext.RemoveRootCommand, RelativeSource={RelativeSource AncestorType=Window}}"
                                             CommandParameter="{Binding}" />
@@ -370,9 +388,9 @@
 
             <GridSplitter Grid.Column="1" Width="5" HorizontalAlignment="Stretch"
                           VerticalAlignment="Stretch" Background="#FFD8D8D8"
-                          ToolTip="拖曳調整面板寬度" />
+                          ToolTip="{loc:Loc Ui.Main.DragResizePanel}" />
 
-            <!-- ─── 3D 視圖 ─── -->
+            <!-- 3D viewport -->
             <h:HelixViewport3D x:Name="viewport" Grid.Column="2"
                                ShowViewCube="True" ShowCoordinateSystem="True"
                                ShowFrameRate="False" ZoomExtentsWhenLoaded="True"
@@ -400,17 +418,16 @@
                 <h:DefaultLights />
             </h:HelixViewport3D>
 
-            <!-- 操作器疊圖層：透明 Viewport3D 疊在主視窗上、永遠最上層。
-                 只在操作器開啟時 IsHitTestVisible（否則空白處滑鼠才會穿透回主視窗） -->
+            <!-- Transparent gizmo overlay above the main viewport. -->
             <Viewport3D x:Name="gizmoOverlay" Grid.Column="2"
                         IsHitTestVisible="{Binding GizmoEnabled}" />
 
             <GridSplitter Grid.Column="3" Width="5" HorizontalAlignment="Stretch"
                           VerticalAlignment="Stretch" Background="#FFD8D8D8"
-                          ToolTip="拖曳調整面板寬度" />
+                          ToolTip="{loc:Loc Ui.Main.DragResizePanel}" />
 
-            <!-- ─── 量測結果面板 ─── -->
-            <GroupBox Grid.Column="4" Header="量測結果" Margin="4">
+            <!-- Measurement results -->
+            <GroupBox Grid.Column="4" Header="{loc:Loc Ui.Main.Measurements}" Margin="4">
                 <ListBox ItemsSource="{Binding Measurements}" HorizontalContentAlignment="Stretch"
                          ScrollViewer.HorizontalScrollBarVisibility="Disabled">
                     <ListBox.ItemTemplate>
@@ -426,7 +443,7 @@
                                                TextWrapping="Wrap" />
                                 </StackPanel>
                                 <Button Grid.Column="1" Content="✕" Width="22" Height="22"
-                                        VerticalAlignment="Top" ToolTip="刪除此筆量測"
+                                        VerticalAlignment="Top" ToolTip="{loc:Loc Ui.Main.DeleteThisMeasurement}"
                                         Command="{Binding DataContext.RemoveMeasurementCommand, RelativeSource={RelativeSource AncestorType=Window}}"
                                         CommandParameter="{Binding}" />
                             </Grid>
diff --git a/src/STPViewer/MainWindow.xaml.cs b/src/STPViewer/MainWindow.xaml.cs
index 2d72ca4..d9f51e7 100644
--- a/src/STPViewer/MainWindow.xaml.cs
+++ b/src/STPViewer/MainWindow.xaml.cs
@@ -18,25 +18,39 @@ public partial class MainWindow : Window
     public MainWindow()
     {
         InitializeComponent();
-        // 版號單一來源 = csproj <Version>；標題執行時讀，避免寫死
-        var v = Assembly.GetExecutingAssembly().GetName().Version!;
-        Title = $"STPViewer V{v.Major}.{v.Minor}.{v.Build} — STP/STEP 3D 檢視器";
+        // Read the version from the project at runtime.
+        UpdateTitle();
         DataContext = _vm;
         _vm.Attach(viewport);
         _vm.AttachOverlay(gizmoOverlay);
         Loaded += MainWindow_Loaded;
         Closing += MainWindow_Closing;
 
-        // 使用者設定：視窗位置大小（View 職責）+ 單位/MRU（VM 職責）
+        // Restore window settings here and units/recent files in the view model.
         _settings = SettingsService.Load();
         ApplyWindowSettings();
         _vm.LoadSettings(_settings);
+        _vm.InitializeLocalization();
+        LocalizationService.Instance.LanguageChanged += LanguageChanged;
+        Closed += (_, _) =>
+        {
+            LocalizationService.Instance.LanguageChanged -= LanguageChanged;
+            _vm.DisposeLocalization();
+        };
 
-        // Gizmo 操作器放在疊圖層；manipulator 會把 MouseUp 標 handled，需 handledEventsToo 才收得到
+        // The gizmo overlay needs handled mouse-up events from the manipulator.
         gizmoOverlay.AddHandler(MouseLeftButtonUpEvent,
             new MouseButtonEventHandler((_, _) => _vm.OnGizmoMouseUp()), handledEventsToo: true);
     }
 
+    private void LanguageChanged(object? sender, System.EventArgs e) => UpdateTitle();
+
+    private void UpdateTitle()
+    {
+        var v = Assembly.GetExecutingAssembly().GetName().Version!;
+        Title = LocalizationService.Format("App.WindowTitle", $"{v.Major}.{v.Minor}.{v.Build}");
+    }
+
     private void ApplyWindowSettings()
     {
         if (_settings.WindowWidth >= 400 && _settings.WindowHeight >= 300)
@@ -44,7 +58,7 @@ public partial class MainWindow : Window
             Width = _settings.WindowWidth;
             Height = _settings.WindowHeight;
         }
-        // 位置要落在目前虛擬桌面內才還原（避免拔掉外接螢幕後視窗開在螢幕外）
+        // Restore the position only when it is within the current virtual desktop.
         if (!double.IsNaN(_settings.WindowLeft) && !double.IsNaN(_settings.WindowTop) &&
             _settings.WindowLeft >= SystemParameters.VirtualScreenLeft - 50 &&
             _settings.WindowTop >= SystemParameters.VirtualScreenTop - 50 &&
@@ -73,7 +87,7 @@ public partial class MainWindow : Window
         SettingsService.Save(_settings);
     }
 
-    /// <summary>支援命令列帶檔開啟：STPViewer.exe a.stp b.stl …</summary>
+    /// <summary>Open files passed on the command line: STPViewer.exe a.stp b.stl …</summary>
     private async void MainWindow_Loaded(object sender, RoutedEventArgs e)
     {
         var files = System.Environment.GetCommandLineArgs().Skip(1)
@@ -82,7 +96,7 @@ public partial class MainWindow : Window
             await _vm.ImportFilesAsync(files);
     }
 
-    /// <summary>Esc / 量測模式快速鍵（焦點在輸入框時不攔截，樹搜尋、剖面數值可正常打字）</summary>
+    /// <summary>Handle Esc and measurement shortcuts without intercepting text inputs.</summary>
     private void Window_PreviewKeyDown(object sender, KeyEventArgs e)
     {
         if (Keyboard.FocusedElement is TextBoxBase or ComboBox) return;
@@ -97,7 +111,7 @@ public partial class MainWindow : Window
             e.Handled = true;
     }
 
-    /// <summary>最近檔案下拉（▾）：即時從 VM 的 MRU 清單組選單</summary>
+    /// <summary>Build the recent-files menu from the view model's current list.</summary>
     private void Recent_Click(object sender, RoutedEventArgs e)
     {
         var menu = new ContextMenu
@@ -107,7 +121,7 @@ public partial class MainWindow : Window
         };
         if (_vm.RecentFiles.Count == 0)
         {
-            menu.Items.Add(new MenuItem { Header = "（沒有最近開啟的檔案）", IsEnabled = false });
+            menu.Items.Add(new MenuItem { Header = LocalizationService.Get("App.NoRecentFiles"), IsEnabled = false });
         }
         else
         {
@@ -131,14 +145,14 @@ public partial class MainWindow : Window
 
     private void Viewport_MouseLeftButtonDown(object sender, MouseButtonEventArgs e)
     {
-        // Shift+左鍵 = 平移（PanGesture2），不觸發量測/拖曳
+        // Shift+left-click pans the view.
         if (Keyboard.Modifiers.HasFlag(ModifierKeys.Shift)) return;
 
         if (_vm.CurrentMode == STPViewer.Models.MeasureMode.Drag)
         {
             if (_vm.OnDragStart(e.GetPosition(viewport.Viewport)))
             {
-                viewport.CaptureMouse(); // 拖出視窗外也持續收到 Move/Up
+                viewport.CaptureMouse(); // Keep receiving move/up events outside the window.
                 e.Handled = true;
             }
             return;
@@ -159,7 +173,7 @@ public partial class MainWindow : Window
     }
 
     private void Viewport_LostMouseCapture(object sender, MouseEventArgs e) =>
-        _vm.OnDragEnd(); // 捕捉意外中斷（Alt+Tab 等）→ 以目前位置定格，不留懸空 Transform
+        _vm.OnDragEnd(); // Commit the current position if capture is interrupted.
 
     private void Window_DragOver(object sender, DragEventArgs e)
     {
diff --git a/src/STPViewer/Models/FaceInfo.cs b/src/STPViewer/Models/FaceInfo.cs
index 7bcfdfb..24b2b8c 100644
--- a/src/STPViewer/Models/FaceInfo.cs
+++ b/src/STPViewer/Models/FaceInfo.cs
@@ -4,13 +4,13 @@ using STPViewer.ViewModels;
 
 namespace STPViewer.Models;
 
-/// <summary>渲染物件（GeometryModel3D）反查 B-rep Face 的對照資料</summary>
+/// <summary>Maps a rendered GeometryModel3D back to a B-rep face.</summary>
 public class FaceInfo
 {
-    /// <summary>B-rep 面；STL 等純網格來源為 null（僅支援點/距離/面距量測）</summary>
+    /// <summary>B-rep face, or null for mesh-only sources such as STL.</summary>
     public Face? BrepFace { get; init; }
 
-    /// <summary>原始（未剖切）三角網格 — 面積計算與剖面還原用；零件平移後會換成新 mesh</summary>
+    /// <summary>Uncut mesh used for area and section restoration; replaced after translation.</summary>
     public required MeshGeometry3D Mesh { get; set; }
 
     public required ModelNodeViewModel Owner { get; init; }
diff --git a/src/STPViewer/Models/LanguageDefinition.cs b/src/STPViewer/Models/LanguageDefinition.cs
new file mode 100644
index 0000000..43fd7ad
--- /dev/null
+++ b/src/STPViewer/Models/LanguageDefinition.cs
@@ -0,0 +1,24 @@
+using CommunityToolkit.Mvvm.ComponentModel;
+
+namespace STPViewer.Models;
+
+public class LanguageDefinition : ObservableObject
+{
+    public string Id { get; }
+    public string Key { get; }
+    public IReadOnlyDictionary<string, string> Data { get; }
+    public bool IsSelected { get; private set; }
+
+    internal LanguageDefinition(string id, string key, IReadOnlyDictionary<string, string> data)
+    {
+        Id = id;
+        Key = key;
+        Data = data;
+    }
+
+    internal void SetSelected(bool selected)
+    {
+        IsSelected = selected;
+        OnPropertyChanged(nameof(IsSelected));
+    }
+}
diff --git a/src/STPViewer/Models/MeasureMode.cs b/src/STPViewer/Models/MeasureMode.cs
index 6c49cb2..5ab2435 100644
--- a/src/STPViewer/Models/MeasureMode.cs
+++ b/src/STPViewer/Models/MeasureMode.cs
@@ -1,6 +1,6 @@
 namespace STPViewer.Models;
 
-/// <summary>量測模式（None = 純瀏覽）</summary>
+/// <summary>Measurement modes; None is the browsing mode.</summary>
 public enum MeasureMode
 {
     None,
@@ -9,11 +9,11 @@ public enum MeasureMode
     Edge,
     Face,
     Circle,
-    Angle,        // 兩面 / 兩邊夾角
-    FaceDistance, // 面到面最短距離（網格近似）
-    Align,        // 兩點對齊：平移零件使點 1 貼到點 2
-    Align3,       // 三點對齊：旋轉+平移（來源 3 點 → 目標 3 點）
-    Drag,         // 拖曳模式：左鍵按住零件沿螢幕平面拖動（放開才烘進 B-rep）
-    Interference, // 干涉檢查結果（非點擊模式，僅作為結果類型）
-    Volume,       // 體積/質心（樹右鍵選單觸發，非點擊模式，僅作為結果類型）
+    Angle,        // Angle between two faces or edges.
+    FaceDistance, // Shortest face-to-face distance (mesh approximation).
+    Align,        // Translate a part so the first point meets the second.
+    Align3,       // Rotate and translate from three source and target points.
+    Drag,         // Move a part in the screen plane; commit on release.
+    Interference, // Result type rather than a picking mode.
+    Volume,       // Volume/centroid result triggered from the tree menu.
 }
diff --git a/src/STPViewer/Models/MeasurementResult.cs b/src/STPViewer/Models/MeasurementResult.cs
index da9ffcf..b1349fb 100644
--- a/src/STPViewer/Models/MeasurementResult.cs
+++ b/src/STPViewer/Models/MeasurementResult.cs
@@ -7,23 +7,23 @@ using HelixToolkit.Wpf;
 namespace STPViewer.Models;
 
 /// <summary>
-/// 一筆量測結果。內部以 mm 儲存原始值，Title/Detail 依目前單位即時產生；
-/// 切換單位時 3D 標籤（DynamicLabels）也同步改字。
+/// A measurement stored in millimeters. Its title, details, and 3D labels
+/// update when the display unit changes.
 /// </summary>
 public class MeasurementResult : ObservableObject
 {
     public MeasureMode Kind { get; init; }
 
-    /// <summary>依單位產生標題（清單粗體列）</summary>
+    /// <summary>Create the list title for a display unit.</summary>
     public required Func<UnitSystem, string> TitleFor { get; init; }
 
-    /// <summary>依單位產生多行明細</summary>
+    /// <summary>Create the detailed text for a display unit.</summary>
     public required Func<UnitSystem, string> DetailFor { get; init; }
 
-    /// <summary>視圖中的標記（刪除量測時一併移除）</summary>
+    /// <summary>View markers removed with this measurement.</summary>
     public List<Visual3D> Overlays { get; } = new();
 
-    /// <summary>單位相關的 3D 文字標籤（切換單位時更新 Text）</summary>
+    /// <summary>3D labels whose text changes with the display unit.</summary>
     public List<(BillboardTextVisual3D Label, Func<UnitSystem, string> TextFor)> DynamicLabels { get; } = new();
 
     private UnitSystem _unit = UnitSystem.Millimeter;
@@ -35,9 +35,14 @@ public class MeasurementResult : ObservableObject
     {
         if (_unit == unit) return;
         _unit = unit;
+        RefreshText();
+    }
+
+    public void RefreshText()
+    {
         OnPropertyChanged(nameof(Title));
         OnPropertyChanged(nameof(Detail));
         foreach ((BillboardTextVisual3D label, Func<UnitSystem, string> textFor) in DynamicLabels)
-            label.Text = textFor(unit);
+            label.Text = textFor(_unit);
     }
 }
diff --git a/src/STPViewer/Models/UnitSystem.cs b/src/STPViewer/Models/UnitSystem.cs
index 0c08b56..9e9e8d6 100644
--- a/src/STPViewer/Models/UnitSystem.cs
+++ b/src/STPViewer/Models/UnitSystem.cs
@@ -8,28 +8,28 @@ public enum UnitSystem
     Inch,
 }
 
-/// <summary>量測值格式化（內部一律 mm，顯示時換算）</summary>
+/// <summary>Format measurements stored in millimeters for the selected display unit.</summary>
 public static class Units
 {
     private const double MmPerInch = 25.4;
 
-    /// <summary>長度</summary>
+    /// <summary>Length.</summary>
     public static string L(double mm, UnitSystem u) =>
         u == UnitSystem.Millimeter ? $"{mm:F3} mm" : $"{mm / MmPerInch:F4} in";
 
-    /// <summary>面積</summary>
+    /// <summary>Area.</summary>
     public static string A(double mm2, UnitSystem u) =>
         u == UnitSystem.Millimeter ? $"{mm2:N3} mm²" : $"{mm2 / (MmPerInch * MmPerInch):N4} in²";
 
-    /// <summary>體積</summary>
+    /// <summary>Volume.</summary>
     public static string V(double mm3, UnitSystem u) =>
         u == UnitSystem.Millimeter ? $"{mm3:N2} mm³" : $"{mm3 / (MmPerInch * MmPerInch * MmPerInch):N4} in³";
 
-    /// <summary>座標分量（無單位字尾）</summary>
+    /// <summary>Coordinate component without a unit suffix.</summary>
     public static string C(double mm, UnitSystem u) =>
         u == UnitSystem.Millimeter ? $"{mm:F3}" : $"{mm / MmPerInch:F4}";
 
-    /// <summary>座標點 (x, y, z)</summary>
+    /// <summary>Coordinate point (x, y, z).</summary>
     public static string P(Point3D p, UnitSystem u) =>
         $"({C(p.X, u)}, {C(p.Y, u)}, {C(p.Z, u)})";
 }
diff --git a/src/STPViewer/STPViewer.csproj b/src/STPViewer/STPViewer.csproj
index 48f1b7e..6ef53bf 100644
--- a/src/STPViewer/STPViewer.csproj
+++ b/src/STPViewer/STPViewer.csproj
@@ -6,7 +6,7 @@
     <Nullable>enable</Nullable>
     <ImplicitUsings>enable</ImplicitUsings>
     <UseWPF>true</UseWPF>
-    <Version>0.7.1</Version>   <!-- 單一版號來源：標題與 publish-winapp 打包資料夾都讀這個 -->
+    <Version>0.7.1</Version>   <!-- Shared by the window title and publish output. -->
   </PropertyGroup>
 
   <ItemGroup>
@@ -15,4 +15,8 @@
     <PackageReference Include="HelixToolkit.Wpf" Version="3.1.2" />
   </ItemGroup>
 
+  <ItemGroup>
+    <None Update="i18n\*.json" CopyToOutputDirectory="PreserveNewest" CopyToPublishDirectory="PreserveNewest" />
+  </ItemGroup>
+
 </Project>
diff --git a/src/STPViewer/Services/InterferenceService.cs b/src/STPViewer/Services/InterferenceService.cs
index 2979d9d..c599b37 100644
--- a/src/STPViewer/Services/InterferenceService.cs
+++ b/src/STPViewer/Services/InterferenceService.cs
@@ -6,8 +6,7 @@ using System.Windows.Media.Media3D;
 namespace STPViewer.Services;
 
 /// <summary>
-/// 干涉檢查結果：Intersects=true 時 Segments 為干涉交線；
-/// false 時 GapA/GapB 為最近點對（網格近似）。
+/// Interference result: Segments holds intersection lines, or GapA/GapB the approximate closest points.
 /// </summary>
 public record InterferenceResult(
     bool Intersects,
@@ -18,10 +17,8 @@ public record InterferenceResult(
     double GapDistance);
 
 /// <summary>
-/// 兩組三角網格的干涉檢查：
-/// 三角形-三角形相交（區間法，回傳交線段）+ 均勻網格空間加速。
-/// 共面接觸（無穿透）不會被判為干涉（近似限制）。
-/// 設計為在背景執行緒呼叫。
+/// Checks intersections between two triangle mesh sets using a uniform spatial grid.
+/// Coplanar contact without penetration is excluded.
 /// </summary>
 public static class InterferenceService
 {
@@ -63,7 +60,7 @@ public static class InterferenceService
         return new InterferenceResult(false, 0, segments, ga, gb, d);
     }
 
-    // ─── 資料結構 ────────────────────────────────────────────────
+    // Spatial data
 
     private readonly struct Triangle
     {
@@ -100,7 +97,7 @@ public static class InterferenceService
         a.Min.Y <= b.Max.Y && a.Max.Y >= b.Min.Y &&
         a.Min.Z <= b.Max.Z && a.Max.Z >= b.Min.Z;
 
-    /// <summary>均勻網格：cell → 三角形索引</summary>
+    /// <summary>Uniform grid from cells to triangle indices.</summary>
     private sealed class TriGrid
     {
         private readonly Dictionary<(int, int, int), List<int>> _cells = new();
@@ -108,7 +105,7 @@ public static class InterferenceService
 
         public TriGrid(Triangle[] tris)
         {
-            // cell 大小：整體對角線 / 64（夾限避免極端值）
+            // Size cells from the scene diagonal, with bounds for extreme sizes.
             Point3D min = tris[0].Min, max = tris[0].Max;
             foreach (Triangle t in tris)
             {
@@ -146,7 +143,7 @@ public static class InterferenceService
         }
     }
 
-    // ─── 三角形相交（區間法，回傳交線段）────────────────────────
+    // Triangle intersection
 
     private static bool TriTriIntersect(in Triangle ta, in Triangle tb, out Point3D s0, out Point3D s1)
     {
@@ -167,12 +164,12 @@ public static class InterferenceService
         if ((db0 > 0 && db1 > 0 && db2 > 0) || (db0 < 0 && db1 < 0 && db2 < 0)) return false;
 
         Vector3D dir = Vector3D.CrossProduct(n1, n2);
-        if (dir.LengthSquared < 1e-24) return false; // 共面：不視為穿透（近似）
+        if (dir.LengthSquared < 1e-24) return false; // Coplanar contact.
 
         if (!PlaneCrossSegment(ta, da0, da1, da2, out Point3D p0, out Point3D p1)) return false;
         if (!PlaneCrossSegment(tb, db0, db1, db2, out Point3D q0, out Point3D q1)) return false;
 
-        // 投影到交線方向取重疊區間
+        // Project onto the intersection direction and overlap the intervals.
         double tp0 = Vector3D.DotProduct(dir, (Vector3D)p0);
         double tp1 = Vector3D.DotProduct(dir, (Vector3D)p1);
         double tq0 = Vector3D.DotProduct(dir, (Vector3D)q0);
@@ -182,14 +179,14 @@ public static class InterferenceService
 
         double lo = Math.Max(tp0, tq0);
         double hi = Math.Min(tp1, tq1);
-        if (lo >= hi) return false; // 無重疊（或僅點接觸）
+        if (lo >= hi) return false;
 
         s0 = LerpOnSegment(p0, p1, tp0, tp1, lo);
         s1 = LerpOnSegment(p0, p1, tp0, tp1, hi);
         return true;
     }
 
-    /// <summary>三角形與平面（頂點符號 d0..d2 已算好）的交線段（兩個交點）</summary>
+    /// <summary>Finds the triangle-plane intersection segment from signed vertex distances.</summary>
     private static bool PlaneCrossSegment(in Triangle t, double d0, double d1, double d2,
         out Point3D p0, out Point3D p1)
     {
@@ -208,8 +205,8 @@ public static class InterferenceService
         Span<Point3D> pts, ref int n)
     {
         if (n >= 3) return;
-        if (da == 0 && db == 0) return;        // 邊在平面上 → 共面情形，略過
-        if (da == 0) { pts[n++] = a; return; } // 頂點剛好在平面上
+        if (da == 0 && db == 0) return;
+        if (da == 0) { pts[n++] = a; return; }
         if (da * db < 0)
             pts[n++] = a + (b - a) * (da / (da - db));
     }
@@ -221,11 +218,11 @@ public static class InterferenceService
         return p0 + (p1 - p0) * f;
     }
 
-    // ─── 無干涉時的近似最小間隙 ─────────────────────────────────
+    // Approximate gap when meshes do not intersect
 
     private static (Point3D a, Point3D b, double d) ApproxMinDistance(Triangle[] trisA, Triangle[] trisB)
     {
-        // 1) 抽樣頂點對頂點求初值
+        // Sample vertices for an initial closest pair.
         double best = double.MaxValue;
         Point3D pa = default, pb = default;
         int strideA = Math.Max(1, trisA.Length / 2000);
@@ -237,14 +234,13 @@ public static class InterferenceService
                 if (d < best) { best = d; pa = trisA[i].A; pb = trisB[j].A; }
             }
 
-        // 2) 以最佳點為中心，精修：點 → 對方所有三角形（AABB 平方距離快速拒絕 + 平行分段，
-        //    初值來自步驟 1 已相當接近 → 絕大多數三角形被 AABB 直接刷掉）
+        // Refine against opposing triangles, rejecting distant AABBs.
         (pb, best) = ClosestOnTriangles(pa, trisB, pb, best);
         (pa, best) = ClosestOnTriangles(pb, trisA, pa, best);
         return (pa, pb, best);
     }
 
-    /// <summary>點 p 到三角形集的最近點（帶初值；回傳更新後的最近點與距離）</summary>
+    /// <summary>Refines the closest point from an initial distance.</summary>
     private static (Point3D pt, double d) ClosestOnTriangles(Point3D p, Triangle[] tris, Point3D seedPt, double seedD)
     {
         object gate = new();
@@ -256,7 +252,7 @@ public static class InterferenceService
             (i, _, local) =>
             {
                 Triangle t = tris[i];
-                // AABB 平方距離下界 ≥ 目前最佳 → 不可能更近，略過（絕大多數三角形在此被刷掉）
+                // Reject triangles whose AABB cannot improve the current distance.
                 double dx = Math.Max(0, Math.Max(t.Min.X - p.X, p.X - t.Max.X));
                 double dy = Math.Max(0, Math.Max(t.Min.Y - p.Y, p.Y - t.Max.Y));
                 double dz = Math.Max(0, Math.Max(t.Min.Z - p.Z, p.Z - t.Max.Z));
@@ -276,7 +272,7 @@ public static class InterferenceService
         return (bestPt, bestD);
     }
 
-    /// <summary>點到三角形最近點（Ericson, Real-Time Collision Detection）</summary>
+    /// <summary>Closest point on a triangle, following Ericson's construction.</summary>
     internal static Point3D ClosestPointOnTriangle(Point3D p, Point3D a, Point3D b, Point3D c)
     {
         Vector3D ab = b - a, ac = c - a, ap = p - a;
diff --git a/src/STPViewer/Services/LocalizationService.cs b/src/STPViewer/Services/LocalizationService.cs
new file mode 100644
index 0000000..6855169
--- /dev/null
+++ b/src/STPViewer/Services/LocalizationService.cs
@@ -0,0 +1,158 @@
+using System.Diagnostics;
+using System.Globalization;
+using System.IO;
+using System.Text.Json;
+using System.Text.Json.Serialization;
+using CommunityToolkit.Mvvm.ComponentModel;
+using STPViewer.Models;
+
+namespace STPViewer.Services;
+
+public class LocalizationService : ObservableObject
+{
+    public static LocalizationService Instance { get; } = new(Path.Combine(AppContext.BaseDirectory, "i18n"));
+
+    private LanguageDefinition? _selected;
+    private readonly LanguageDefinition? _english;
+
+    public IReadOnlyList<LanguageDefinition> Languages { get; }
+    public string Language => _selected?.Id ?? "";
+    public event EventHandler? LanguageChanged;
+
+    public LocalizationService(string directory)
+    {
+        Languages = LoadLanguages(directory);
+        _english = Languages.FirstOrDefault(language => language.Id == "en");
+        _selected = Languages.FirstOrDefault(language => language.Id == ResolveLanguage(null));
+        foreach (LanguageDefinition language in Languages)
+            language.SetSelected(ReferenceEquals(language, _selected));
+    }
+
+    public string this[string key]
+    {
+        get
+        {
+            if (_selected?.Data.TryGetValue(key, out string? value) == true) return value;
+            if (_english?.Data.TryGetValue(key, out value) == true) return value;
+            return key;
+        }
+    }
+
+    public static string Get(string key) => Instance[key];
+
+    public static string Format(string key, params object[] args) => Instance.FormatText(key, args);
+
+    public string FormatText(string key, params object[] args)
+    {
+        string text = this[key];
+        try
+        {
+            return string.Format(CultureInfo.CurrentCulture, text, args);
+        }
+        catch (FormatException ex)
+        {
+            Trace.TraceWarning($"Invalid translation format '{key}' in '{Language}': {ex.Message}");
+            if (_english?.Data.TryGetValue(key, out string? fallback) == true && fallback != text)
+            {
+                try { return string.Format(CultureInfo.CurrentCulture, fallback, args); }
+                catch (FormatException) { }
+            }
+            return key;
+        }
+    }
+
+    public string ResolveLanguage(string? language)
+    {
+        string id = NormalizeId(language ?? CultureInfo.CurrentUICulture.Name);
+        if (Languages.Any(item => item.Id == id)) return id;
+
+        string[] parts = id.Split('_');
+        if (parts[0] == "zh")
+        {
+            bool traditional = parts.Any(part => part is "hant" or "tw" or "hk" or "mo");
+            string[] candidates = traditional ? ["zh_tw", "zh_hant", "zh"] : ["zh_cn", "zh_hans", "zh"];
+            foreach (string candidate in candidates)
+                if (Languages.Any(item => item.Id == candidate)) return candidate;
+            return _english?.Id ?? Languages.FirstOrDefault()?.Id ?? "";
+        }
+
+        LanguageDefinition? match = Languages.FirstOrDefault(item => item.Id == parts[0]);
+        return match?.Id ?? _english?.Id ?? Languages.FirstOrDefault()?.Id ?? "";
+    }
+
+    public void SetLanguage(string? language)
+    {
+        string id = ResolveLanguage(language);
+        LanguageDefinition? selected = Languages.FirstOrDefault(item => item.Id == id);
+        bool changed = !ReferenceEquals(_selected, selected);
+        _selected = selected;
+
+        foreach (LanguageDefinition item in Languages)
+            item.SetSelected(ReferenceEquals(item, selected));
+
+        if (selected is not null)
+        {
+            try
+            {
+                CultureInfo culture = CultureInfo.GetCultureInfo(selected.Id.Replace('_', '-'));
+                CultureInfo.CurrentUICulture = culture;
+                CultureInfo.DefaultThreadCurrentUICulture = culture;
+            }
+            catch (CultureNotFoundException) { }
+        }
+
+        if (!changed) return;
+        OnPropertyChanged(nameof(Language));
+        OnPropertyChanged("Item[]");
+        LanguageChanged?.Invoke(this, EventArgs.Empty);
+    }
+
+    private static string NormalizeId(string id) => id.Trim().Replace('-', '_').ToLowerInvariant();
+
+    private static IReadOnlyList<LanguageDefinition> LoadLanguages(string directory)
+    {
+        var languages = new List<LanguageDefinition>();
+        if (!Directory.Exists(directory)) return languages;
+
+        string[] paths;
+        try
+        {
+            paths = Directory.GetFiles(directory, "*.json");
+        }
+        catch (Exception ex) when (ex is IOException or UnauthorizedAccessException)
+        {
+            Trace.TraceWarning($"Cannot read language directory '{directory}': {ex.Message}");
+            return languages;
+        }
+
+        foreach (string path in paths.OrderBy(path => path, StringComparer.Ordinal))
+        {
+            try
+            {
+                LanguageFile? file = JsonSerializer.Deserialize<LanguageFile>(File.ReadAllText(path));
+                string id = NormalizeId(Path.GetFileNameWithoutExtension(path));
+                if (string.IsNullOrWhiteSpace(file?.Key) || file.Data is null || id.Length == 0 ||
+                    file.Data.Any(pair => string.IsNullOrWhiteSpace(pair.Key) || pair.Value is null))
+                    throw new JsonException("Expected a display key and a data object containing string translations.");
+                if (languages.Any(language => language.Id == id))
+                    throw new JsonException($"Duplicate language identifier '{id}'.");
+
+                languages.Add(new LanguageDefinition(id, file.Key, file.Data));
+            }
+            catch (Exception ex) when (ex is IOException or UnauthorizedAccessException or JsonException)
+            {
+                Trace.TraceWarning($"Cannot load language file '{path}': {ex.Message}");
+            }
+        }
+        return languages;
+    }
+
+    private sealed class LanguageFile
+    {
+        [JsonPropertyName("key")]
+        public string? Key { get; set; }
+
+        [JsonPropertyName("data")]
+        public Dictionary<string, string>? Data { get; set; }
+    }
+}
diff --git a/src/STPViewer/Services/MeasurementService.cs b/src/STPViewer/Services/MeasurementService.cs
index 1c86b35..17402a6 100644
--- a/src/STPViewer/Services/MeasurementService.cs
+++ b/src/STPViewer/Services/MeasurementService.cs
@@ -6,16 +6,17 @@ using CADability;
 using CADability.GeoObject;
 using HelixToolkit.Wpf;
 using STPViewer.Models;
+using static STPViewer.Services.LocalizationService;
 
 namespace STPViewer.Services;
 
-/// <summary>角度量測的單次拾取：邊方向或面法向量</summary>
+/// <summary>One direction selected for angle measurement.</summary>
 public record DirectionPick(Point3D At, Vector3D Direction, string Desc);
 
 /// <summary>
-/// 點/距離/邊/面/圓/角度/面距 量測幾何計算 + 視圖 overlay 產生。
-/// 邊長、圓半徑以 B-rep 精確值為準；面積與面距用三角網格近似。
-/// 所有文字以 Func&lt;UnitSystem,string&gt; 延後產生，支援 mm/inch 即時切換。
+/// Computes measurements and their viewport overlays.
+/// B-rep provides exact edge lengths and radii; mesh values are approximate.
+/// Text is deferred so unit and language changes update existing results.
 /// </summary>
 public class MeasurementService
 {
@@ -29,13 +30,11 @@ public class MeasurementService
     private static GeoPoint ToGeo(Point3D p) => new(p.X, p.Y, p.Z);
     private static Point3D ToP3(GeoPoint p) => new(p.x, p.y, p.z);
 
-    // ─── 拾取輔助 ────────────────────────────────────────────────
+    // Picking
 
     /// <summary>
-    /// 命中點吸附：點到圓形邊附近（容差內）→ 吸附**圓心**（量兩孔 pitch 的關鍵，v0.5.0）；
-    /// 否則吸附最近的 B-rep 頂點（容差內）；都沒有 → 回傳原始表面點。
-    /// 圓心與頂點都在容差內時，比「命中點到圓形邊」與「命中點到頂點」誰近（圓弧端點常與圓重疊，
-    /// 點在圓邊上時圓心優先勝出才符合直覺）。
+    /// Snaps to the nearest vertex or circular edge within tolerance.
+    /// A circular edge snaps to its center for hole pitch measurements.
     /// </summary>
     public Point3D Snap(FaceInfo fi, Point3D hit, double tolerance)
     {
@@ -51,9 +50,9 @@ public class MeasurementService
                 if (d < bestD) { bestD = d; best = p; }
             }
         }
-        catch { /* 頂點存取失敗則不吸附 */ }
+        catch { }
 
-        // 圓形邊：以「命中點到邊曲線」的距離參與比較，勝出時吸附到圓心
+        // Compare distance to the circle edge before selecting its center.
         try
         {
             foreach (Edge e in fi.BrepFace.AllEdges)
@@ -67,19 +66,18 @@ public class MeasurementService
                 if (d < bestD) { bestD = d; best = ToP3(el.Center); }
             }
         }
-        catch { /* 邊存取失敗則維持頂點吸附結果 */ }
+        catch { }
         return best;
     }
 
     /// <summary>
-    /// 角度量測拾取：命中點附近有直線邊（容差內）→ 邊方向；
-    /// 否則取面法向量（B-rep 精確；無 B-rep 時用網格法向量）。
+    /// Uses a nearby straight edge for direction, otherwise a face normal.
     /// </summary>
     public DirectionPick PickDirection(FaceInfo fi, Point3D hit, Vector3D meshNormal, double tolerance)
     {
         if (fi.BrepFace is not null)
         {
-            // 1) 近距離直線邊優先
+            // Prefer a nearby straight edge.
             try
             {
                 foreach (Edge e in fi.BrepFace.AllEdges)
@@ -91,28 +89,28 @@ public class MeasurementService
                     {
                         Vector3D dir = ToP3(ln.EndPoint) - ToP3(ln.StartPoint);
                         dir.Normalize();
-                        return new DirectionPick(p, dir, "邊方向");
+                        return new DirectionPick(p, dir, "Runtime.DirectionEdge");
                     }
                 }
             }
             catch { }
 
-            // 2) 面法向量（精確）
+            // Use the B-rep face normal when available.
             try
             {
                 GeoPoint2D uv = fi.BrepFace.Surface.PositionOf(ToGeo(hit));
                 GeoVector n = fi.BrepFace.Surface.GetNormal(uv).Normalized;
-                return new DirectionPick(hit, new Vector3D(n.x, n.y, n.z), "面法向量");
+                return new DirectionPick(hit, new Vector3D(n.x, n.y, n.z), "Runtime.DirectionFace");
             }
             catch { }
         }
         Vector3D mn = meshNormal;
         if (mn.LengthSquared < 1e-12) mn = new Vector3D(0, 0, 1);
         mn.Normalize();
-        return new DirectionPick(hit, mn, "面法向量（網格）");
+        return new DirectionPick(hit, mn, "Runtime.DirectionMeshFace");
     }
 
-    // ─── 點 / 距離 ───────────────────────────────────────────────
+    // Point and distance
 
     public MeasurementResult MeasurePoint(Point3D p, string label, double markerR)
     {
@@ -134,8 +132,7 @@ public class MeasurementService
         {
             Kind = MeasureMode.Distance,
             TitleFor = u => $"{label}  {Units.L(d.Length, u)}",
-            DetailFor = u => $"距離 = {Units.L(d.Length, u)}\nΔX = {Units.L(d.X, u)}\nΔY = {Units.L(d.Y, u)}\nΔZ = {Units.L(d.Z, u)}\n" +
-                             $"P1 {Units.P(p1, u)}\nP2 {Units.P(p2, u)}",
+            DetailFor = u => Format("Runtime.DistanceDetail", Units.L(d.Length, u), Units.L(d.X, u), Units.L(d.Y, u), Units.L(d.Z, u), Units.P(p1, u), Units.P(p2, u)),
         };
         r.Overlays.Add(Sphere(p1, markerR));
         r.Overlays.Add(Sphere(p2, markerR));
@@ -149,9 +146,9 @@ public class MeasurementService
         return r;
     }
 
-    // ─── 邊 / 圓 ─────────────────────────────────────────────────
+    // Edge and circle
 
-    /// <summary>量測命中面上最近的邊。circlesOnly=true 時只找圓形邊。找不到回傳 null。</summary>
+    /// <summary>Measures the nearest edge, or the nearest circular edge when circlesOnly is true.</summary>
     public MeasurementResult? MeasureEdge(FaceInfo fi, Point3D hit, string label, double markerR, bool circlesOnly)
     {
         if (fi.BrepFace is null) return null;
@@ -193,9 +190,7 @@ public class MeasurementService
         {
             Kind = MeasureMode.Circle,
             TitleFor = u => $"{label}  ⌀{Units.L(radius * 2, u)}",
-            DetailFor = u => $"直徑 = {Units.L(radius * 2, u)}\n半徑 = {Units.L(radius, u)}\n" +
-                             $"{(full ? "周長" : "弧長")} = {Units.L(curveLen, u)}\n" +
-                             $"圓心 {Units.P(center, u)}",
+            DetailFor = u => Format("Runtime.CircleDetail", Units.L(radius * 2, u), Units.L(radius, u), Get(full ? "Runtime.Circumference" : "Runtime.ArcLength"), Units.L(curveLen, u), Units.P(center, u)),
         };
         r.Overlays.Add(Polyline(curve, HighlightColor, 3));
         r.Overlays.Add(Sphere(center, markerR));
@@ -219,8 +214,7 @@ public class MeasurementService
         {
             Kind = MeasureMode.Edge,
             TitleFor = u => $"{label}  L = {Units.L(len, u)}",
-            DetailFor = u => $"長度 = {Units.L(len, u)}\nΔX = {Units.C(d.X, u)}  ΔY = {Units.C(d.Y, u)}  ΔZ = {Units.C(d.Z, u)}\n" +
-                             $"起點 {Units.P(s, u)}\n終點 {Units.P(e, u)}",
+            DetailFor = u => Format("Runtime.LineDetail", Units.L(len, u), Units.C(d.X, u), Units.C(d.Y, u), Units.C(d.Z, u), Units.P(s, u), Units.P(e, u)),
         };
         r.Overlays.Add(new LinesVisual3D
         {
@@ -241,32 +235,32 @@ public class MeasurementService
         {
             Kind = MeasureMode.Edge,
             TitleFor = u => $"{label}  L = {Units.L(len, u)}",
-            DetailFor = u => $"曲線長 = {Units.L(len, u)}\n類型 = {typeName}",
+            DetailFor = u => Format("Runtime.CurveDetail", Units.L(len, u), typeName),
         };
         r.Overlays.Add(Polyline(curve, HighlightColor, 3));
         AddLabel(r, ToP3(curve.PointAt(0.5)) + new Vector3D(0, 0, markerR * 2), u => $"L={Units.L(len, u)}");
         return r;
     }
 
-    // ─── 面 ──────────────────────────────────────────────────────
+    // Face
 
     public MeasurementResult MeasureFace(FaceInfo fi, Point3D hit, string label, double markerR)
     {
-        // 面積：三角網格加總（近似值，三角化精度內）
+        // Area is estimated from the triangle mesh.
         double area = MeshArea(fi.Mesh);
         int triCount = fi.Mesh.TriangleIndices.Count / 3;
         Func<UnitSystem, string> surfaceDesc = fi.BrepFace is not null
             ? DescribeSurface(fi.BrepFace.Surface)
-            : _ => "類型 = 網格（無 B-rep）";
+            : _ => Get("Runtime.MeshSurface");
 
         var r = new MeasurementResult
         {
             Kind = MeasureMode.Face,
             TitleFor = u => $"{label}  A ≈ {Units.A(area, u)}",
-            DetailFor = u => $"面積 ≈ {Units.A(area, u)}（網格近似）\n{surfaceDesc(u)}\n三角形數 = {triCount:N0}",
+            DetailFor = u => Format("Runtime.FaceDetail", Units.A(area, u), surfaceDesc(u), triCount),
         };
 
-        // overlay：外輪廓 highlight + 標籤
+        // Highlight the outer edges and add a label.
         if (fi.BrepFace is not null)
         {
             try
@@ -302,35 +296,33 @@ public class MeasurementService
             case PlaneSurface ps:
             {
                 GeoVector n = ps.Normal.Normalized;
-                string desc = $"類型 = 平面\n法向量 ({n.x:F3}, {n.y:F3}, {n.z:F3})";
-                return _ => desc;
+                return _ => Format("Runtime.PlaneSurface", n.x, n.y, n.z);
             }
             case CylindricalSurface cs:
             {
                 GeoVector ax = cs.Axis.Normalized;
                 double radius = cs.RadiusX;
-                return u => $"類型 = 圓柱面\n半徑 = {Units.L(radius, u)}\n軸向 ({ax.x:F3}, {ax.y:F3}, {ax.z:F3})";
+                return u => Format("Runtime.CylinderSurface", Units.L(radius, u), ax.x, ax.y, ax.z);
             }
             default:
             {
-                string desc = $"類型 = {SurfaceTypeName(surface)}";
-                return _ => desc;
+                return _ => Format("Runtime.SurfaceType", SurfaceTypeName(surface));
             }
         }
     }
 
     private static string SurfaceTypeName(ISurface s) => s.GetType().Name switch
     {
-        "SphericalSurface" => "球面",
-        "ToroidalSurface" => "環面",
-        "ConicalSurface" => "圓錐面",
-        "NurbsSurface" => "NURBS 曲面",
-        "SurfaceOfRevolution" => "旋轉曲面",
-        "SurfaceOfLinearExtrusion" => "拉伸曲面",
+        "SphericalSurface" => Get("Runtime.SphericalSurface"),
+        "ToroidalSurface" => Get("Runtime.ToroidalSurface"),
+        "ConicalSurface" => Get("Runtime.ConicalSurface"),
+        "NurbsSurface" => Get("Runtime.NurbsSurface"),
+        "SurfaceOfRevolution" => Get("Runtime.RevolutionSurface"),
+        "SurfaceOfLinearExtrusion" => Get("Runtime.ExtrusionSurface"),
         var other => other,
     };
 
-    // ─── 角度（兩面 / 兩邊夾角）─────────────────────────────────
+    // Angle
 
     public MeasurementResult MeasureAngle(DirectionPick a, DirectionPick b, string label, double markerR, double arrowLen)
     {
@@ -343,10 +335,7 @@ public class MeasurementService
         {
             Kind = MeasureMode.Angle,
             TitleFor = _ => $"{label}  ∠ {deg:F2}°",
-            DetailFor = _ => $"夾角 = {deg:F2}°（補角 {comp:F2}°）\n" +
-                             $"方向 1：{a.Desc} ({a.Direction.X:F3}, {a.Direction.Y:F3}, {a.Direction.Z:F3})\n" +
-                             $"方向 2：{b.Desc} ({b.Direction.X:F3}, {b.Direction.Y:F3}, {b.Direction.Z:F3})\n" +
-                             "（兩面夾角以法向量計，互補角請參考補角值）",
+            DetailFor = _ => Format("Runtime.AngleDetail", deg, comp, Get(a.Desc), a.Direction.X, a.Direction.Y, a.Direction.Z, Get(b.Desc), b.Direction.X, b.Direction.Y, b.Direction.Z),
         };
         r.Overlays.Add(Sphere(a.At, markerR));
         r.Overlays.Add(Sphere(b.At, markerR));
@@ -368,7 +357,7 @@ public class MeasurementService
         Thickness = 2,
     };
 
-    // ─── 面到面最短距離（網格近似）──────────────────────────────
+    // Face distance
 
     public MeasurementResult MeasureFaceDistance(FaceInfo a, FaceInfo b, string label, double markerR)
     {
@@ -378,9 +367,7 @@ public class MeasurementService
         {
             Kind = MeasureMode.FaceDistance,
             TitleFor = u => $"{label}  min = {Units.L(d.Length, u)}",
-            DetailFor = u => $"最短距離 ≈ {Units.L(d.Length, u)}（網格近似）\n" +
-                             $"ΔX = {Units.L(d.X, u)}\nΔY = {Units.L(d.Y, u)}\nΔZ = {Units.L(d.Z, u)}\n" +
-                             $"點 1 {Units.P(pa, u)}\n點 2 {Units.P(pb, u)}",
+            DetailFor = u => Format("Runtime.FaceDistanceDetail", Units.L(d.Length, u), Units.L(d.X, u), Units.L(d.Y, u), Units.L(d.Z, u), Units.P(pa, u), Units.P(pb, u)),
         };
         r.Overlays.Add(Sphere(pa, markerR));
         r.Overlays.Add(Sphere(pb, markerR));
@@ -394,7 +381,7 @@ public class MeasurementService
         return r;
     }
 
-    /// <summary>兩網格最近點對：頂點→三角形雙向（頂點過多時抽樣，結果為近似值）</summary>
+    /// <summary>Approximates the closest points by probing vertices against triangles in both directions.</summary>
     private static (Point3D a, Point3D b) MeshMinDistance(MeshGeometry3D ma, MeshGeometry3D mb)
     {
         double best = double.MaxValue;
@@ -427,19 +414,18 @@ public class MeasurementService
         return (pa, pb);
     }
 
-    // ─── 體積 / 質心（封閉網格 signed volume）────────────────────
+    // Volume and centroid
 
     /// <summary>
-    /// 網格體積與質心：各三角形與原點構成的四面體有向體積加總（divergence theorem）。
-    /// 只對「封閉」網格有意義（開放殼會得到不可靠的值 → IsClosedReliable=false 供呼叫端提示）。
-    /// 多個 mesh（多實體）直接加總。
+    /// Computes signed volume and centroid from origin-based tetrahedra.
+    /// The result is reliable only for closed meshes.
     /// </summary>
     public static (double VolumeMm3, Point3D Centroid, bool Reliable) MeshVolume(
         System.Collections.Generic.IEnumerable<MeshGeometry3D> meshes)
     {
-        double vol6 = 0;                       // Σ 6×有向體積
-        double absVol6 = 0;                    // Σ |6×有向體積|（封閉性 sanity check 用）
-        double cx = 0, cy = 0, cz = 0;         // Σ 四面體質心 × 6×有向體積
+        double vol6 = 0;
+        double absVol6 = 0;
+        double cx = 0, cy = 0, cz = 0;
         foreach (MeshGeometry3D mesh in meshes)
         {
             Point3DCollection pos = mesh.Positions;
@@ -453,14 +439,14 @@ public class MeasurementService
                          + a.Z * (b.X * c.Y - b.Y * c.X);
                 vol6 += v;
                 absVol6 += Math.Abs(v);
-                // 四面體（a,b,c,原點）質心 = (a+b+c)/4
+                // Tetrahedron centroid = (a + b + c) / 4.
                 cx += (a.X + b.X + c.X) / 4 * v;
                 cy += (a.Y + b.Y + c.Y) / 4 * v;
                 cz += (a.Z + b.Z + c.Z) / 4 * v;
             }
         }
         double volume = Math.Abs(vol6) / 6;
-        // 有向體積相對正負抵銷比例過高 → 可能是開放殼/法向不一致，數值不可靠
+        // Large signed cancellation suggests an open mesh or inconsistent normals.
         bool reliable = absVol6 > 0 && Math.Abs(vol6) / absVol6 > 0.01 && volume > 1e-9;
         Point3D centroid = Math.Abs(vol6) > 1e-12
             ? new Point3D(cx / vol6, cy / vol6, cz / vol6)
@@ -468,7 +454,7 @@ public class MeasurementService
         return (volume, centroid, reliable);
     }
 
-    // 點到三角形最近點：共用 InterferenceService.ClosestPointOnTriangle（v0.4.0 去重複）
+    // Shares the triangle closest-point calculation with InterferenceService.
 
     // ─── overlay helpers ─────────────────────────────────────────
 
diff --git a/src/STPViewer/Services/RigidAlign.cs b/src/STPViewer/Services/RigidAlign.cs
index 0c113b7..b889971 100644
--- a/src/STPViewer/Services/RigidAlign.cs
+++ b/src/STPViewer/Services/RigidAlign.cs
@@ -4,15 +4,14 @@ using System.Windows.Media.Media3D;
 namespace STPViewer.Services;
 
 /// <summary>
-/// 三點對齊 / 旋轉的剛體變換數學。
-/// 同一個變換需要兩種表示：WPF <see cref="Matrix3D"/>（列向量約定，給網格/邊線）與
-/// CADability <see cref="CADability.ModOp"/>（行向量約定，給 B-rep Modify）— 用 <see cref="ToModOp"/> 轉換。
+/// Rigid transformations for three-point alignment and rotation.
+/// <see cref="ToModOp"/> converts WPF <see cref="Matrix3D"/> to CADability's matrix convention.
 /// </summary>
 public static class RigidAlign
 {
     /// <summary>
-    /// 來源 3 點 → 目標 3 點 的剛體變換（不縮放）：
-    /// p1→q1 精確貼合、p1p2 方向對齊 q1q2、三點平面對齊。共線/退化回傳 false。
+    /// Computes a rigid transform from three source points to three target points.
+    /// Returns false for collinear or degenerate points.
     /// </summary>
     public static bool TryRigidTransform(
         Point3D p1, Point3D p2, Point3D p3,
@@ -22,7 +21,7 @@ public static class RigidAlign
         if (!TryFrame(p1, p2, p3, out Vector3D xp, out Vector3D yp, out Vector3D zp)) return false;
         if (!TryFrame(q1, q2, q3, out Vector3D xq, out Vector3D yq, out Vector3D zq)) return false;
 
-        // R = Bq · Bpᵀ（行向量約定）；WPF Matrix3D 為列向量約定 → 轉置擺放
+        // R = Bq · Bpᵀ, transposed for Matrix3D's convention.
         double R(int r, int c)
         {
             double xpc = c == 0 ? xp.X : c == 1 ? xp.Y : xp.Z;
@@ -47,7 +46,7 @@ public static class RigidAlign
         return true;
     }
 
-    /// <summary>WPF Matrix3D（列向量約定）→ CADability ModOp（行向量約定，3×4）</summary>
+    /// <summary>Converts a WPF matrix to a CADability ModOp.</summary>
     public static CADability.ModOp ToModOp(Matrix3D m) => new(new double[3, 4]
     {
         { m.M11, m.M21, m.M31, m.OffsetX },
@@ -58,7 +57,7 @@ public static class RigidAlign
     public static bool Collinear(Point3D a, Point3D b, Point3D c) =>
         Vector3D.CrossProduct(b - a, c - a).LengthSquared < 1e-12;
 
-    /// <summary>三點 → 正交座標架（x=1→2 方向、z=平面法向、y=z×x）；共線回傳 false</summary>
+    /// <summary>Builds an orthogonal frame from three points; returns false for collinear points.</summary>
     private static bool TryFrame(Point3D a, Point3D b, Point3D c,
         out Vector3D x, out Vector3D y, out Vector3D z)
     {
diff --git a/src/STPViewer/Services/SectionService.cs b/src/STPViewer/Services/SectionService.cs
index abea6e5..b11f68f 100644
--- a/src/STPViewer/Services/SectionService.cs
+++ b/src/STPViewer/Services/SectionService.cs
@@ -4,8 +4,8 @@ using System.Windows.Media.Media3D;
 namespace STPViewer.Services;
 
 /// <summary>
-/// 剖面：把三角網格 / 線段集用半空間裁切（保留 dot(p - p0, n) ≤ 0 的一側）。
-/// WPF 3D 沒有 GPU clip plane，採 CPU 裁切後置換 Geometry（原始 mesh 保留可還原）。
+/// Clips meshes and line segments to the half-space dot(p - p0, n) ≤ 0.
+/// The original geometry remains available for restoration.
 /// </summary>
 public static class SectionService
 {
@@ -23,7 +23,7 @@ public static class SectionService
         Point3DCollection pos = src.Positions;
         Int32Collection idx = src.TriangleIndices;
 
-        // 頂點距離快取
+        // Cache signed distances for each vertex.
         var dist = new double[pos.Count];
         for (int i = 0; i < pos.Count; i++)
             dist[i] = Vector3D.DotProduct(pos[i] - planePoint, normal);
@@ -47,7 +47,7 @@ public static class SectionService
                 continue;
             }
 
-            // 部分在保留側：Sutherland-Hodgman 裁出 3 或 4 邊形，扇形分割
+            // Clip the polygon and triangulate it as a fan.
             int n = 0;
             for (int k = 0; k < 3; k++)
             {
@@ -78,7 +78,7 @@ public static class SectionService
         idx.Add(i); idx.Add(i + 1); idx.Add(i + 2);
     }
 
-    /// <summary>裁切線段集（成對端點）</summary>
+    /// <summary>Clips paired line segment endpoints.</summary>
     public static Point3DCollection ClipSegments(Point3DCollection segments, Point3D planePoint, Vector3D normal)
     {
         var result = new Point3DCollection();
diff --git a/src/STPViewer/Services/SettingsService.cs b/src/STPViewer/Services/SettingsService.cs
index 139cdfc..9a5cb77 100644
--- a/src/STPViewer/Services/SettingsService.cs
+++ b/src/STPViewer/Services/SettingsService.cs
@@ -5,7 +5,7 @@ using System.Text.Json;
 
 namespace STPViewer.Services;
 
-/// <summary>使用者設定（%LOCALAPPDATA%\STPViewer\settings.json）</summary>
+/// <summary>User settings stored in %LOCALAPPDATA%\STPViewer\settings.json.</summary>
 public class AppSettings
 {
     public double WindowWidth { get; set; } = double.NaN;
@@ -14,13 +14,14 @@ public class AppSettings
     public double WindowTop { get; set; } = double.NaN;
     public bool WindowMaximized { get; set; }
     public bool UseInch { get; set; }
+    public string? Language { get; set; }
     public List<string> RecentFiles { get; set; } = new();
 
-    /// <summary>快速工具列顯示的按鈕 key 清單；null = 用預設（QuickBarViewModel.Registry）</summary>
+    /// <summary>Visible quick bar keys; null uses registry defaults.</summary>
     public List<string>? QuickBarKeys { get; set; }
 }
 
-/// <summary>設定讀寫：壞檔/缺檔一律回預設值，儲存失敗靜默（設定不值得讓程式閃退）</summary>
+/// <summary>Loads defaults for missing or invalid settings and ignores save failures.</summary>
 public static class SettingsService
 {
     public const int MaxRecentFiles = 10;
@@ -36,7 +37,7 @@ public static class SettingsService
             if (File.Exists(SettingsPath))
                 return JsonSerializer.Deserialize<AppSettings>(File.ReadAllText(SettingsPath)) ?? new AppSettings();
         }
-        catch { /* 壞檔回預設 */ }
+        catch { }
         return new AppSettings();
     }
 
@@ -48,6 +49,6 @@ public static class SettingsService
             File.WriteAllText(SettingsPath,
                 JsonSerializer.Serialize(settings, new JsonSerializerOptions { WriteIndented = true }));
         }
-        catch { /* 儲存失敗靜默 */ }
+        catch { }
     }
 }
diff --git a/src/STPViewer/Services/StepImportService.cs b/src/STPViewer/Services/StepImportService.cs
index 24cc893..7b3118f 100644
--- a/src/STPViewer/Services/StepImportService.cs
+++ b/src/STPViewer/Services/StepImportService.cs
@@ -6,28 +6,31 @@ using System.Windows.Media;
 using System.Windows.Media.Media3D;
 using CADability;
 using CADability.GeoObject;
-using IOPath = System.IO.Path; // CADability.GeoObject.Path（曲線）撞名
+using IOPath = System.IO.Path;
+using static STPViewer.Services.LocalizationService;
 
 namespace STPViewer.Services;
 
-/// <summary>單一 B-rep Face 的三角網格（mesh 已 Freeze，可跨執行緒）；STL 來源 BrepFace 為 null</summary>
+/// <summary>A frozen triangle mesh for one B-rep face; BrepFace is null for STL.</summary>
 public record ImportedFace(Face? BrepFace, MeshGeometry3D Mesh);
 
-/// <summary>匯入後的階層節點：group（裝配）或 leaf（零件幾何）</summary>
+/// <summary>An imported assembly group or geometry leaf.</summary>
 public class ImportedNode
 {
     public string Name { get; set; } = "";
+    public string? NameKey { get; set; }
+    public int NameNumber { get; set; }
     public List<ImportedNode> Children { get; } = new();
 
-    // ── leaf 幾何 ──
+    // Leaf geometry
     public List<ImportedFace> Faces { get; } = new();
-    public Point3DCollection? EdgeSegments { get; set; }   // 輪廓線（成對端點，已 Freeze）
-    public bool HasBrep { get; set; } = true;              // STL / 純曲線 = false
+    public Point3DCollection? EdgeSegments { get; set; }   // Frozen paired endpoints.
+    public bool HasBrep { get; set; } = true;              // False for STL and curves.
 
-    /// <summary>來源 B-rep 物件（Solid/Shell/Face/曲線）— 零件平移時整體 Modify 用</summary>
+    /// <summary>Source B-rep objects used for whole-part transforms.</summary>
     public List<CADability.GeoObject.IGeoObject> SourceGeos { get; } = new();
 
-    // ── 統計（group 節點由 Aggregate 彙總）──
+    // Group totals are calculated by Aggregate.
     public int SolidCount { get; set; }
     public int FaceCount { get; set; }
     public int TriangleCount { get; set; }
@@ -39,29 +42,35 @@ public class ImportedNode
 public record ImportedFileData(string FilePath, ImportedNode Root);
 
 /// <summary>
-/// CAD 檔匯入（STEP / STL / DXF）。STEP 以 HierarchyToBlocks 還原裝配樹。
-/// 設計為在背景執行緒呼叫；回傳的 Freezable 全部已 Freeze。
+/// Imports STEP, STL and DXF files on a background thread.
+/// Returned WPF Freezables are frozen.
 /// </summary>
 public class StepImportService
 {
-    /// <summary>匯入階段回報（耗時分解），UI 可顯示於狀態列；null 則靜默</summary>
+    /// <summary>Import progress for the status bar.</summary>
     public Action<string>? Progress { get; set; }
+    public Action<Func<string>>? ProgressTextFor { get; set; }
 
-    private long _triTicks, _edgeTicks; // 三角化 / 邊取樣 累計耗時（TimeSpan ticks，避免逐面 ms 截斷歸零）
+    private void ReportProgress(Func<string> textFor)
+    {
+        Progress?.Invoke(textFor());
+        ProgressTextFor?.Invoke(textFor);
+    }
+
+    private long _triTicks, _edgeTicks; // Accumulated tessellation and edge sampling ticks.
     private double TriMs => new TimeSpan(_triTicks).TotalMilliseconds;
     private double EdgeMs => new TimeSpan(_edgeTicks).TotalMilliseconds;
 
-    /// <summary>延後的 leaf 幾何工作（三角化+邊取樣）：樹走訪時收集，之後平行執行。
-    /// 平行粒度 = 整個 leaf（同 leaf 的面共用 Edge，不可面級平行）。</summary>
+    /// <summary>Geometry work queued per leaf, then run in parallel. Faces within a leaf share edges.</summary>
     private readonly List<Action> _leafWork = new();
 
-    /// <summary>平行三角化偶發失敗的面（CADability 跨 leaf 仍有少量共享狀態）→ 平行結束後循序重試</summary>
+    /// <summary>Faces to retry sequentially after parallel tessellation.</summary>
     private readonly System.Collections.Concurrent.ConcurrentBag<(ImportedNode Leaf, HashSet<Edge> EdgeSet, List<(Face F, double Prec)> Failed)> _retry = new();
 
     public ImportedFileData Import(string filePath)
     {
         if (!File.Exists(filePath))
-            throw new FileNotFoundException("找不到檔案", filePath);
+            throw new FileNotFoundException(Get("Runtime.FileNotFound"), filePath);
 
         _triTicks = _edgeTicks = 0;
         _leafWork.Clear();
@@ -73,21 +82,22 @@ public class StepImportService
             case ".stl": ImportStlFile(filePath, root); break;
             case ".dxf": ImportDxfFile(filePath, root); break;
             default:
-                throw new InvalidDataException("不支援的格式（支援 .stp / .step / .stl / .dxf；CADability 無 IGES reader）");
+                throw new InvalidDataException(Get("Runtime.UnsupportedFormat"));
         }
 
         if (_leafWork.Count > 0)
         {
             var sw = System.Diagnostics.Stopwatch.StartNew();
-            Progress?.Invoke($"三角化 {_leafWork.Count} 個零件（平行）…");
+            int leafCount = _leafWork.Count;
+            ReportProgress(() => Format("Runtime.Triangulating", leafCount));
             System.Threading.Tasks.Parallel.ForEach(_leafWork, w =>
             {
                 try { w(); }
-                catch { /* 個別零件失敗不讓整檔失敗 */ }
+                catch { }
             });
             _leafWork.Clear();
 
-            // 平行下偶發失敗的面：競爭已結束，循序重試一輪（FinishLeaf 也延到此時才跑）
+            // Retry failed faces sequentially after the parallel pass.
             int retried = 0;
             foreach ((ImportedNode leaf, HashSet<Edge> edgeSet, var failed) in _retry)
             {
@@ -96,14 +106,16 @@ public class StepImportService
                 FinishLeaf(leaf, edgeSet);
             }
             _retry.Clear();
-            Progress?.Invoke($"幾何處理 {sw.ElapsedMilliseconds:N0} ms" +
-                $"（三角化 {TriMs:N0} ms、邊取樣 {EdgeMs:N0} ms{(retried > 0 ? $"、重試補回 {retried} 面" : "")}）");
+            long elapsed = sw.ElapsedMilliseconds;
+            int retryCount = retried;
+            ReportProgress(() => Format("Runtime.GeometryProcessed", elapsed, TriMs, EdgeMs,
+                retryCount > 0 ? Format("Runtime.RetriedFaces", retryCount) : ""));
         }
 
         Prune(root);
         Aggregate(root);
         if (root.SolidCount == 0 && root.FaceCount == 0 && CountSegments(root) == 0)
-            throw new InvalidDataException("檔案內沒有可顯示的幾何");
+            throw new InvalidDataException(Get("Runtime.NoGeometry"));
         return new ImportedFileData(filePath, root);
     }
 
@@ -114,29 +126,25 @@ public class StepImportService
 
     private void ImportStepFile(string path, ImportedNode root)
     {
-        Progress?.Invoke("解析 STEP（大檔可能需數分鐘）…");
+        ReportProgress(() => Get("Runtime.ParsingStep"));
         var sw = System.Diagnostics.Stopwatch.StartNew();
         var importer = new ImportStep { HierarchyToBlocks = true };
         GeoObjectList list = importer.Read(path)
-            ?? throw new InvalidDataException("CADability 無法解析此 STEP 檔");
-        Progress?.Invoke($"STEP 解析 {sw.ElapsedMilliseconds:N0} ms");
+            ?? throw new InvalidDataException(Get("Runtime.StepParseFailed"));
+        long elapsed = sw.ElapsedMilliseconds;
+        ReportProgress(() => Format("Runtime.StepParsed", elapsed));
         BuildChildren(root, EnumerateGeo(list));
     }
 
-    // ─── STL（純網格，無 B-rep）──
-    // 直接解析三角形（StlMeshReader），**不經過 CADability**。CADability 的 ImportSTL 會為每個
-    // 三角形建一個 B-rep Face（含 Edge/Vertex 拓樸），百萬三角形需數十分鐘且吃光記憶體
-    // （實測 100k 三角形：CADability ~41 s，直接解析 ~11 ms）。STL 本就無 B-rep，讀三角形即可。
-    // ⚠️ 因此 STL leaf 沒有 SourceGeos（CADability B-rep）→ 不進 STEP 匯出（本就非 STEP B-rep 幾何）；
-    //    剛體變換仍走網格層（TransformRoot 的 SourceGeos 迴圈空轉、mesh 照樣變換），量測走網格近似不受影響。
+    // STL is read directly as mesh geometry without B-rep objects.
 
     private void ImportStlFile(string path, ImportedNode root)
     {
-        Progress?.Invoke("解析 STL（直接讀三角形）…");
+        ReportProgress(() => Get("Runtime.ParsingStl"));
         var sw = System.Diagnostics.Stopwatch.StartNew();
         List<StlMeshReader.MeshGroup> groups = StlMeshReader.Read(path);
         if (groups.Count == 0)
-            throw new InvalidDataException("STL 檔內沒有三角形");
+            throw new InvalidDataException(Get("Runtime.StlNoTriangles"));
 
         foreach (StlMeshReader.MeshGroup g in groups)
         {
@@ -149,30 +157,34 @@ public class StepImportService
             var leaf = new ImportedNode
             {
                 Name = g.Name,
+                NameKey = g.NameKey,
+                NameNumber = g.NameNumber,
                 HasBrep = false,
                 SolidCount = 1,
-                FaceCount = tris,      // STL 無 B-rep 面 → 以三角形數代表
+                FaceCount = tris,
                 TriangleCount = tris,
                 Bounds = BoundsOfMesh(mesh),
             };
             leaf.Faces.Add(new ImportedFace(null, mesh));
             root.Children.Add(leaf);
         }
-        Progress?.Invoke($"STL 解析 {sw.ElapsedMilliseconds:N0} ms（{root.Children.Count} 個網格）");
+        long elapsed = sw.ElapsedMilliseconds;
+        int meshCount = root.Children.Count;
+        ReportProgress(() => Format("Runtime.StlParsed", elapsed, meshCount));
     }
 
-    // ─── DXF（多為線架構；Solid/Face 走同一套，曲線取樣成線段）──
+    // DXF
 
     private void ImportDxfFile(string path, ImportedNode root)
     {
         var import = new CADability.DXF.Import(path);
         Project project = import.Project
-            ?? throw new InvalidDataException("無法解析 DXF 檔");
+            ?? throw new InvalidDataException(Get("Runtime.DxfParseFailed"));
         Model model = project.GetActiveModel();
         BuildChildren(root, EnumerateGeo(model.AllObjects));
     }
 
-    // ─── 階層走訪 ────────────────────────────────────────────────
+    // Assembly traversal
 
     private static IEnumerable<IGeoObject> EnumerateGeo(System.Collections.IEnumerable list)
     {
@@ -189,7 +201,7 @@ public class StepImportService
     private void BuildChildren(ImportedNode parent, IEnumerable<IGeoObject> objects)
     {
         var looseFaces = new List<Face>();
-        var looseCurves = new List<IGeoObject>(); // 皆為 ICurve
+        var looseCurves = new List<IGeoObject>();
 
         foreach (IGeoObject go in objects)
         {
@@ -219,7 +231,7 @@ public class StepImportService
 
         if (looseFaces.Count > 0)
         {
-            var leaf = new ImportedNode { Name = "面" };
+            var leaf = new ImportedNode { Name = Get("Runtime.FaceName"), NameKey = "Runtime.FaceName" };
             leaf.SourceGeos.AddRange(looseFaces);
             _leafWork.Add(() =>
             {
@@ -233,7 +245,7 @@ public class StepImportService
                 if (failed.Count > 0) _retry.Add((leaf, edgeSet, failed));
                 else FinishLeaf(leaf, edgeSet);
             });
-            parent.Children.Add(leaf); // 三角化延後，空 leaf 由 Prune 收掉
+            parent.Children.Add(leaf);
         }
         if (looseCurves.Count > 0)
         {
@@ -243,7 +255,8 @@ public class StepImportService
                 segs.Freeze();
                 var leaf = new ImportedNode
                 {
-                    Name = "曲線",
+                    Name = Get("Runtime.CurveName"),
+                    NameKey = "Runtime.CurveName",
                     HasBrep = false,
                     EdgeSegments = segs,
                     Bounds = BoundsOfPoints(segs),
@@ -256,28 +269,39 @@ public class StepImportService
 
     private ImportedNode? BlockNode(Block block)
     {
-        // Block 只有單一同名 Solid → 折疊成 leaf（STEP 常見的 product→solid 包裝）
+        // Collapse a block containing one solid into a leaf.
         if (block.NumChildren == 1 && block.Child(0) is Solid s)
         {
             ImportedNode leaf = SolidNode(s);
-            if (!string.IsNullOrWhiteSpace(block.Name)) leaf.Name = block.Name;
+            if (!string.IsNullOrWhiteSpace(block.Name))
+            {
+                leaf.Name = block.Name;
+                leaf.NameKey = null;
+                leaf.NameNumber = 0;
+            }
             return leaf;
         }
 
         var node = new ImportedNode
         {
-            Name = string.IsNullOrWhiteSpace(block.Name) ? "組件" : block.Name,
+            Name = string.IsNullOrWhiteSpace(block.Name) ? Get("Runtime.ComponentName") : block.Name,
+            NameKey = string.IsNullOrWhiteSpace(block.Name) ? "Runtime.ComponentName" : null,
         };
         BuildChildren(node, ChildrenOf(block));
         if (node.Children.Count == 0) return null;
 
-        // 單鏈折疊：group 只有一個子節點且名稱相同/空白 → 去掉中間層
+        // Drop a redundant group when it has one child with the same name.
         if (node.Children.Count == 1)
         {
             ImportedNode only = node.Children[0];
             if (string.IsNullOrWhiteSpace(only.Name) || only.Name == node.Name)
             {
-                only.Name = node.Name;
+                if (node.NameKey is null || only.NameKey is not null || string.IsNullOrWhiteSpace(only.Name))
+                {
+                    only.Name = node.Name;
+                    only.NameKey = node.NameKey;
+                    only.NameNumber = node.NameNumber;
+                }
                 return only;
             }
         }
@@ -288,7 +312,8 @@ public class StepImportService
     {
         var leaf = new ImportedNode
         {
-            Name = string.IsNullOrWhiteSpace(solid.NameOrEmpty) ? "Solid" : solid.NameOrEmpty,
+            Name = string.IsNullOrWhiteSpace(solid.NameOrEmpty) ? Get("Runtime.SolidName") : solid.NameOrEmpty,
+            NameKey = string.IsNullOrWhiteSpace(solid.NameOrEmpty) ? "Runtime.SolidName" : null,
             SolidCount = 1,
         };
         leaf.SourceGeos.Add(solid);
@@ -312,7 +337,8 @@ public class StepImportService
     {
         var leaf = new ImportedNode
         {
-            Name = string.IsNullOrWhiteSpace(shell.NameOrEmpty) ? "Shell" : shell.NameOrEmpty,
+            Name = string.IsNullOrWhiteSpace(shell.NameOrEmpty) ? Get("Runtime.ShellName") : shell.NameOrEmpty,
+            NameKey = string.IsNullOrWhiteSpace(shell.NameOrEmpty) ? "Runtime.ShellName" : null,
         };
         leaf.SourceGeos.Add(shell);
         _leafWork.Add(() =>
@@ -328,7 +354,7 @@ public class StepImportService
         return leaf;
     }
 
-    // ─── 幾何處理 ────────────────────────────────────────────────
+    // Geometry processing
 
     private static BoundingCube SafeBounds(Func<BoundingCube> get)
     {
@@ -336,7 +362,7 @@ public class StepImportService
         catch { return new BoundingCube(); }
     }
 
-    /// <summary>三角化精度依物件大小調整：對角線 × 0.0015，限制在 [0.02, 0.5] mm</summary>
+    /// <summary>Tessellation precision: bounding diagonal × 0.0015, clamped to [0.02, 0.5] mm.</summary>
     private static double PrecisionFor(BoundingCube bc)
     {
         double diag;
@@ -346,7 +372,7 @@ public class StepImportService
         return Math.Clamp(diag * 0.0015, 0.02, 0.5);
     }
 
-    /// <returns>false = 三角化失敗（平行下偶發，可循序重試）</returns>
+    /// <returns>False when tessellation fails and the face needs a retry.</returns>
     private bool AddFace(Face face, double precision, ImportedNode leaf, HashSet<Edge> edgeSet)
     {
         GeoPoint[] points; int[] indices;
@@ -357,7 +383,7 @@ public class StepImportService
         }
         catch
         {
-            return false; // 個別面三角化失敗時跳過，不讓整檔失敗
+            return false;
         }
         finally
         {
@@ -381,11 +407,11 @@ public class StepImportService
         {
             foreach (Edge e in face.AllEdges) edgeSet.Add(e);
         }
-        catch { /* 邊收集失敗不影響面渲染 */ }
+        catch { }
         return true;
     }
 
-    /// <summary>leaf 收尾：邊取樣 + 統計 + 邊界</summary>
+    /// <summary>Completes edge sampling, counts and bounds for one leaf.</summary>
     private void FinishLeaf(ImportedNode leaf, HashSet<Edge> edgeSet)
     {
         var sw = System.Diagnostics.Stopwatch.StartNew();
@@ -422,7 +448,7 @@ public class StepImportService
         return segments;
     }
 
-    /// <summary>把曲線取樣成線段對（直線 1 段、曲線 12 段）</summary>
+    /// <summary>Samples curves into paired line endpoints.</summary>
     private static void AppendCurveSegments(Point3DCollection segments, ICurve curve)
     {
         int n = curve is Line ? 1 : 12;
@@ -437,7 +463,7 @@ public class StepImportService
                 prev = cur;
             }
         }
-        catch { /* 個別曲線取樣失敗跳過 */ }
+        catch { }
     }
 
     private static Rect3D BoundsOfMesh(MeshGeometry3D mesh) => BoundsOfPoints(mesh.Positions);
@@ -457,7 +483,7 @@ public class StepImportService
             Math.Max(maxX - minX, 1e-6), Math.Max(maxY - minY, 1e-6), Math.Max(maxZ - minZ, 1e-6));
     }
 
-    /// <summary>移除沒有任何幾何的節點（延後三角化全失敗的 leaf、因此變空的 group）</summary>
+    /// <summary>Removes nodes left empty after tessellation.</summary>
     private static void Prune(ImportedNode node)
     {
         for (int i = node.Children.Count - 1; i >= 0; i--)
@@ -469,7 +495,7 @@ public class StepImportService
         }
     }
 
-    /// <summary>group 節點統計彙總（bottom-up）</summary>
+    /// <summary>Aggregates counts and bounds from children.</summary>
     private static void Aggregate(ImportedNode node)
     {
         if (node.IsLeaf) return;
diff --git a/src/STPViewer/Services/StlExportService.cs b/src/STPViewer/Services/StlExportService.cs
index d01f809..c8a16d0 100644
--- a/src/STPViewer/Services/StlExportService.cs
+++ b/src/STPViewer/Services/StlExportService.cs
@@ -11,27 +11,22 @@ using CADability.GeoObject;
 namespace STPViewer.Services;
 
 /// <summary>
-/// 網格精度：Current = 目前顯示網格；Fine = 由 B-rep 以較細精度重新三角化（無 B-rep 的來源維持現有網格）。
-/// 不提供「較粗」：CADability 的 GetTriangulation 對「比快取粗」的精度要求會直接回傳既有較細快取，
-/// 匯入時已三角化過 → 要求粗化實際上拿到同一份網格（實測驗證），故誠實不提供。
+/// Mesh quality: Current uses the displayed mesh; Fine retessellates B-rep geometry.
 /// </summary>
 public enum StlMeshQuality { Current, Fine }
 
 /// <summary>
-/// STL 匯出：WPF 三角網格 → binary / ASCII STL。
-/// STL 本身無單位，約定輸出 mm（scale=1）；inch 交接用 scale = 1/25.4。
+/// Writes WPF triangle meshes as binary or ASCII STL; scale=1 uses millimeters.
 /// </summary>
 public static class StlExportService
 {
     /// <summary>
-    /// 三角化精度係數（相對匯入預設）：Fine 較細（三角形多、曲面平滑）。
-    /// 實測 CADability 三角形數對精度非單調（0.4× 重算反而比 1× 少 — 重算網格較有效率），
-    /// 要明顯更細需 ≤0.15×（test.stp：1× = 30,784 → 0.1× = 42,220 三角形）。
+    /// Tessellation factor relative to import precision; 0.15 produces a finer mesh.
     /// </summary>
     public static double PrecisionFactor(StlMeshQuality q) =>
         q == StlMeshQuality.Fine ? 0.15 : 1.0;
 
-    /// <summary>預估檔案大小：binary = 84 + 50×n；ASCII 每三角形約 230 bytes</summary>
+    /// <summary>Estimated file size: 84 + 50 bytes per binary triangle, about 230 per ASCII triangle.</summary>
     public static long EstimateBytes(long triangles, bool ascii) =>
         ascii ? 20 + triangles * 230 : 84 + triangles * 50;
 
@@ -44,8 +39,7 @@ public static class StlExportService
     };
 
     /// <summary>
-    /// 把多個網格寫成一個 STL 檔。退化（零面積）三角形濾除。
-    /// 回傳實際寫出的三角形數。
+    /// Writes meshes to one STL file, skipping zero-area triangles. Returns the triangle count.
     /// </summary>
     public static int Write(string path, IReadOnlyList<MeshGeometry3D> meshes, bool ascii, double scale) =>
         ascii ? WriteAscii(path, meshes, scale) : WriteBinary(path, meshes, scale);
@@ -55,11 +49,11 @@ public static class StlExportService
         using var fs = new FileStream(path, FileMode.Create, FileAccess.Write, FileShare.None, 1 << 16);
         using var bw = new BinaryWriter(fs);
 
-        // 80-byte header（不可以 "solid" 開頭，部分讀取器會誤判為 ASCII）
+        // Avoid "solid" in the header; some readers would mistake it for ASCII.
         var header = new byte[80];
         Encoding.ASCII.GetBytes("STPViewer binary STL (unit: mm x scale)").CopyTo(header, 0);
         bw.Write(header);
-        bw.Write(0u); // 三角形數 placeholder，寫完回頭補
+        bw.Write(0u); // Backfilled after writing triangles.
 
         int count = 0;
         foreach (MeshGeometry3D mesh in meshes)
@@ -69,7 +63,7 @@ public static class StlExportService
             for (int i = 0; i + 2 < idx.Count; i += 3)
             {
                 Point3D a = pos[idx[i]], b = pos[idx[i + 1]], c = pos[idx[i + 2]];
-                if (!TryNormal(a, b, c, out Vector3D n)) continue; // 退化三角形
+                if (!TryNormal(a, b, c, out Vector3D n)) continue;
                 bw.Write((float)n.X); bw.Write((float)n.Y); bw.Write((float)n.Z);
                 WriteVertex(bw, a, scale);
                 WriteVertex(bw, b, scale);
@@ -125,7 +119,7 @@ public static class StlExportService
         sw.WriteLine(string.Format(inv, "      vertex {0:e6} {1:e6} {2:e6}",
             p.X * scale, p.Y * scale, p.Z * scale));
 
-    /// <returns>false = 退化三角形（面積 ≈ 0）</returns>
+    /// <returns>False for a zero-area triangle.</returns>
     private static bool TryNormal(Point3D a, Point3D b, Point3D c, out Vector3D n)
     {
         n = Vector3D.CrossProduct(b - a, c - a);
@@ -135,12 +129,11 @@ public static class StlExportService
         return true;
     }
 
-    // ─── B-rep 重新三角化（精細/較粗匯出用）────────────────────────
+    // B-rep retessellation
 
     /// <summary>
-    /// 由 B-rep 幾何以指定精度係數重新三角化，回傳每面一個 frozen mesh。
-    /// CADability 非執行緒安全 → 呼叫端維持循序（可在單一背景執行緒）。
-    /// 個別面三角化失敗時跳過（與匯入一致的容錯策略）。
+    /// Retessellates B-rep geometry into frozen meshes, one per face.
+    /// Call sequentially because CADability tessellation is not thread-safe.
     /// </summary>
     public static List<MeshGeometry3D> Tessellate(IEnumerable<IGeoObject> geos, double precisionFactor)
     {
@@ -170,9 +163,7 @@ public static class StlExportService
     }
 
     /// <summary>
-    /// 匯入預設精度（與 StepImportService.PrecisionFor 同款 clamp）再乘 factor —
-    /// 先 clamp 再乘，保證 factor&lt;1 時嚴格比匯入快取細（否則大殼在匯入被 0.5 上限截住，
-    /// 直接乘在 clamp 前會算出比快取粗的值 → CADability 回傳快取、精細無效）。
+    /// Clamp the import precision before applying factor so Fine is finer than the cached mesh.
     /// </summary>
     private static double PrecisionFor(BoundingCube bc, double factor)
     {
diff --git a/src/STPViewer/Services/StlMeshReader.cs b/src/STPViewer/Services/StlMeshReader.cs
index 1a1ad72..e71a6aa 100644
--- a/src/STPViewer/Services/StlMeshReader.cs
+++ b/src/STPViewer/Services/StlMeshReader.cs
@@ -8,15 +8,13 @@ using System.Windows.Media.Media3D;
 namespace STPViewer.Services;
 
 /// <summary>
-/// 直接解析 STL 三角網格（binary / ASCII）→ WPF mesh，**不經過 CADability**。
-/// CADability 的 ImportSTL 會為每個三角形建一個 B-rep Face（含 Edge/Vertex 拓樸），
-/// 大檔（百萬三角形）需數十分鐘且吃光記憶體；STL 本就無 B-rep，直接讀三角形即可。
-/// 實測 100k 三角形：CADability 約 41,000 ms，直接解析約 11 ms。
+/// Reads binary and ASCII STL triangles directly into WPF meshes.
 /// </summary>
 public static class StlMeshReader
 {
-    /// <summary>一個 solid 區塊的網格（頂點未焊接：每三角形 3 個獨立頂點，與 STL 原生一致）</summary>
-    public record MeshGroup(string Name, Point3DCollection Positions, Int32Collection Indices);
+    /// <summary>Mesh for one solid section; vertices remain unwelded.</summary>
+    public record MeshGroup(string Name, Point3DCollection Positions, Int32Collection Indices,
+        string? NameKey = null, int NameNumber = 0);
 
     public static List<MeshGroup> Read(string path)
     {
@@ -24,13 +22,12 @@ public static class StlMeshReader
     }
 
     /// <summary>
-    /// binary STL 判定：檔案大小必須剛好等於 84 + 50×count（count = offset 80 的 uint32）。
-    /// 這是最可靠的判別法 — binary 的 80-byte header 常也以 "solid" 開頭，不能只看開頭字串。
+    /// Binary STL has exactly 84 + 50 × triangle count bytes; its header may also start with "solid".
     /// </summary>
     private static bool IsBinary(string path)
     {
         var fi = new FileInfo(path);
-        if (fi.Length < 84) return false; // 太小，當 ASCII 讓後續拋有意義的錯
+        if (fi.Length < 84) return false;
         Span<byte> head = stackalloc byte[84];
         using (FileStream fs = File.OpenRead(path))
         {
@@ -58,8 +55,8 @@ public static class StlMeshReader
         int off = 84, vi = 0;
         for (uint t = 0; t < count; t++)
         {
-            if (off + 50 > bytes.Length) break; // 檔案被截斷：保住已解析的部分
-            off += 12; // 跳過 normal（渲染用不到；WPF 自算法向）
+            if (off + 50 > bytes.Length) break;
+            off += 12; // WPF computes the normal.
             for (int v = 0; v < 3; v++)
             {
                 float x = BitConverter.ToSingle(span[off..]);
@@ -71,12 +68,11 @@ public static class StlMeshReader
             }
             off += 2; // attribute byte count
         }
-        return new List<MeshGroup> { new("網格", positions, indices) };
+        return new List<MeshGroup> { new(LocalizationService.Get("Runtime.MeshName"), positions, indices, "Runtime.MeshName") };
     }
 
     /// <summary>
-    /// ASCII STL：逐行掃 "vertex x y z"，每 3 個湊成一個三角形；"solid &lt;name&gt;" 起新群組。
-    /// ASCII 大檔罕見（同樣三角數約為 binary 的 5 倍體積），故以正確性為主。
+    /// ASCII STL: read vertex triples and start a new group at each solid section.
     /// </summary>
     private static List<MeshGroup> ReadAscii(string path)
     {
@@ -88,7 +84,8 @@ public static class StlMeshReader
         void FlushGroup()
         {
             if (pos is { Count: > 0 } && idx is not null)
-                groups.Add(new MeshGroup(groups.Count == 0 ? "網格" : $"網格 {groups.Count + 1}", pos, idx));
+                groups.Add(new MeshGroup(groups.Count == 0 ? LocalizationService.Get("Runtime.MeshName") : LocalizationService.Format("Runtime.MeshNameNumbered", groups.Count + 1), pos, idx,
+                    groups.Count == 0 ? "Runtime.MeshName" : "Runtime.MeshNameNumbered", groups.Count + 1));
             pos = null; idx = null; vi = 0;
         }
 
diff --git a/src/STPViewer/StlExportDialog.xaml b/src/STPViewer/StlExportDialog.xaml
index 5daaf18..02d3356 100644
--- a/src/STPViewer/StlExportDialog.xaml
+++ b/src/STPViewer/StlExportDialog.xaml
@@ -2,8 +2,9 @@
         xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
         xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
         xmlns:vm="clr-namespace:STPViewer.ViewModels"
-        Title="匯出 STL — 參數設定"
-        Width="440" SizeToContent="Height"
+        xmlns:loc="clr-namespace:STPViewer.Localization"
+        Title="{loc:Loc Ui.StlExport.Title}"
+        Width="520" SizeToContent="Height"
         WindowStartupLocation="CenterOwner"
         ResizeMode="NoResize" ShowInTaskbar="False"
         d:DataContext="{d:DesignInstance Type=vm:StlExportViewModel}"
@@ -38,38 +39,38 @@
             </Style>
         </Grid.Resources>
 
-        <TextBlock Grid.Row="0" Grid.Column="0" Text="匯出範圍" />
+        <TextBlock Grid.Row="0" Grid.Column="0" Text="{loc:Loc Ui.StlExport.Scope}" />
         <ComboBox Grid.Row="0" Grid.Column="1" SelectedIndex="{Binding ScopeIndex}"
-                  ToolTip="STL 無裝配結構；合併 = 所有可見零件進同一檔">
-            <ComboBoxItem Content="全部可見檔案 → 合併成單一 STL" />
-            <ComboBoxItem Content="每個可見檔案 → 各一個 STL" />
+                  ToolTip="{loc:Loc Ui.StlExport.ScopeTooltip}">
+            <ComboBoxItem Content="{loc:Loc Ui.StlExport.ScopeMerge}" />
+            <ComboBoxItem Content="{loc:Loc Ui.StlExport.ScopePerFile}" />
         </ComboBox>
 
-        <TextBlock Grid.Row="1" Grid.Column="0" Text="格式" />
+        <TextBlock Grid.Row="1" Grid.Column="0" Text="{loc:Loc Ui.StlExport.Format}" />
         <ComboBox Grid.Row="1" Grid.Column="1" SelectedIndex="{Binding FormatIndex}">
-            <ComboBoxItem Content="Binary（建議，檔案小）" />
-            <ComboBoxItem Content="ASCII（文字可讀，檔案約 4 倍大）" />
+            <ComboBoxItem Content="{loc:Loc Ui.StlExport.FormatBinary}" />
+            <ComboBoxItem Content="{loc:Loc Ui.StlExport.FormatAscii}" />
         </ComboBox>
 
-        <TextBlock Grid.Row="2" Grid.Column="0" Text="單位縮放" />
+        <TextBlock Grid.Row="2" Grid.Column="0" Text="{loc:Loc Ui.StlExport.UnitScale}" />
         <ComboBox Grid.Row="2" Grid.Column="1" SelectedIndex="{Binding UnitIndex}"
-                  ToolTip="STL 檔本身無單位；內部幾何為 mm，選 inch 會把座標 ÷25.4">
-            <ComboBoxItem Content="mm（1:1，預設）" />
-            <ComboBoxItem Content="inch（座標 ÷ 25.4）" />
-            <ComboBoxItem Content="自訂縮放係數…" />
+                  ToolTip="{loc:Loc Ui.StlExport.UnitTooltip}">
+            <ComboBoxItem Content="{loc:Loc Ui.StlExport.UnitMillimeter}" />
+            <ComboBoxItem Content="{loc:Loc Ui.StlExport.UnitInch}" />
+            <ComboBoxItem Content="{loc:Loc Ui.StlExport.UnitCustom}" />
         </ComboBox>
 
         <TextBox Grid.Row="3" Grid.Column="1" Text="{Binding CustomScaleText, UpdateSourceTrigger=PropertyChanged}"
                  Margin="0,0,0,10" Padding="4,2"
                  Visibility="{Binding IsCustomScale, Converter={StaticResource BoolToVis}}"
-                 ToolTip="座標乘上此係數（例：0.001 = mm→m）" />
+                 ToolTip="{loc:Loc Ui.StlExport.CustomScaleTooltip}" />
 
-        <TextBlock Grid.Row="4" Grid.Column="0" Text="網格精度" />
+        <TextBlock Grid.Row="4" Grid.Column="0" Text="{loc:Loc Ui.StlExport.MeshQuality}" />
         <ComboBox Grid.Row="4" Grid.Column="1" SelectedIndex="{Binding QualityIndex}"
                   IsEnabled="{Binding HasBrep}"
-                  ToolTip="精細會由 B-rep 重新三角化（僅 STEP 來源；STL/DXF 維持現有網格），大組件需要時間">
-            <ComboBoxItem Content="目前顯示網格（快，與畫面一致）" />
-            <ComboBoxItem Content="精細 — 重新三角化，曲面更平滑（慢、檔案大）" />
+                  ToolTip="{loc:Loc Ui.StlExport.QualityTooltip}">
+            <ComboBoxItem Content="{loc:Loc Ui.StlExport.QualityCurrent}" />
+            <ComboBoxItem Content="{loc:Loc Ui.StlExport.QualityFine}" />
         </ComboBox>
 
         <Border Grid.Row="5" Grid.ColumnSpan="2" Background="#F0F4F8" CornerRadius="4"
@@ -78,8 +79,8 @@
         </Border>
 
         <StackPanel Grid.Row="6" Grid.ColumnSpan="2" Orientation="Horizontal" HorizontalAlignment="Right">
-            <Button Content="取消" Width="80" Margin="0,0,8,0" IsCancel="True" />
-            <Button Content="匯出…" Width="96" IsDefault="True"
+            <Button Content="{loc:Loc Ui.StlExport.Cancel}" Width="80" Margin="0,0,8,0" IsCancel="True" />
+            <Button Content="{loc:Loc Ui.StlExport.Export}" Width="96" IsDefault="True"
                     IsEnabled="{Binding CanConfirm}" Click="Confirm_Click" />
         </StackPanel>
     </Grid>
diff --git a/src/STPViewer/StlExportDialog.xaml.cs b/src/STPViewer/StlExportDialog.xaml.cs
index bb3b0f2..7ad9081 100644
--- a/src/STPViewer/StlExportDialog.xaml.cs
+++ b/src/STPViewer/StlExportDialog.xaml.cs
@@ -3,7 +3,7 @@ using STPViewer.ViewModels;
 
 namespace STPViewer;
 
-/// <summary>STL 匯出參數對話框 — 選項邏輯在 StlExportViewModel，這裡只做確認/取消</summary>
+/// <summary>STL export settings dialog; the view model owns the options.</summary>
 public partial class StlExportDialog : Window
 {
     public StlExportViewModel ViewModel { get; }
diff --git a/src/STPViewer/ViewModels/MainViewModel.Drag.cs b/src/STPViewer/ViewModels/MainViewModel.Drag.cs
index baf2a4f..f91f8b7 100644
--- a/src/STPViewer/ViewModels/MainViewModel.Drag.cs
+++ b/src/STPViewer/ViewModels/MainViewModel.Drag.cs
@@ -2,25 +2,26 @@ using System.Windows;
 using System.Windows.Media.Media3D;
 using HelixToolkit.Wpf;
 using STPViewer.Models;
+using static STPViewer.Services.LocalizationService;
 
 namespace STPViewer.ViewModels;
 
-// ─── 拖曳模式（左鍵按住零件沿螢幕平面拖；放開才烘進 B-rep）──────────
+// Drag mode
 public partial class MainViewModel
 {
-    // 拖曳模式：暫時 Transform 跟著滑鼠，放開才一次性烘進 B-rep（TranslateRoot）
+    // Preview with a transform, then commit to B-rep on release.
     private ModelNodeViewModel? _dragRoot;
-    private Point3D _dragAnchor;              // 命中點（世界座標），拖曳平面的錨點
-    private Vector3D _dragApplied;            // 目前累計位移
+    private Point3D _dragAnchor;
+    private Vector3D _dragApplied;
     private TranslateTransform3D? _dragTransform;
 
-    /// <summary>左鍵按下：命中零件則開始拖曳（回傳 true 表示要捕捉滑鼠）</summary>
+    /// <summary>Starts dragging a hit part; returns true when the mouse should be captured.</summary>
     public bool OnDragStart(Point position)
     {
         if (_viewport is null || IsBusy || CurrentMode != MeasureMode.Drag || _dragRoot is not null)
             return false;
 
-        // 兩種渲染內容都可能在場：合併網格查 _mergedMap、逐面（剖面時）查 _faceMap
+        // Hits can come from merged meshes or section faces.
         ModelNodeViewModel? leaf = null;
         Point3D anchor = default;
         foreach (var h in _viewport.Viewport.FindHits(position))
@@ -41,14 +42,14 @@ public partial class MainViewModel
             if (l.BodyVisual is not null)
                 l.BodyVisual.Transform = _dragTransform;
 
-        // 拖曳中隱藏邊線（LinesVisual3D 隨 Transform 變更逐幀重建會卡）
+        // Hide edges while moving to avoid rebuilding them each frame.
         _edgesSuspended = true;
         SetEdgesActive(false);
-        StatusText = $"拖曳「{root.Name}」中…（放開定位）";
+        SetStatus(() => Format("Runtime.Dragging", root.Name));
         return true;
     }
 
-    /// <summary>滑鼠移動：把 2D 位移投影到「過錨點、面向相機」的平面上 → 暫時 Transform</summary>
+    /// <summary>Projects pointer movement onto the camera-facing plane through the anchor.</summary>
     public void OnDragMove(Point position)
     {
         if (_viewport?.Camera is not System.Windows.Media.Media3D.ProjectionCamera cam ||
@@ -62,15 +63,14 @@ public partial class MainViewModel
         _dragTransform.OffsetZ = _dragApplied.Z;
     }
 
-    /// <summary>放開：移除暫時 Transform，一次性烘進 B-rep（量測精度不受拖曳影響）</summary>
+    /// <summary>Commits the temporary transform to B-rep on release.</summary>
     public bool OnDragEnd()
     {
         if (_dragRoot is null) return false;
         ModelNodeViewModel root = _dragRoot;
         Vector3D delta = _dragApplied;
 
-        // 清除暫時位移：必須用 Identity，不可用 null —— HelixToolkit GetTransform 對 child.Transform
-        // 不做 null 檢查（Children.Add(null) 會拋「無法新增空值到集合中」），下次 FindHits 即 crash
+        // HelixToolkit hit testing requires Identity rather than a null transform.
         foreach (ModelNodeViewModel l in root.Leaves())
             if (l.BodyVisual is not null)
                 l.BodyVisual.Transform = Transform3D.Identity;
@@ -78,12 +78,12 @@ public partial class MainViewModel
         _dragTransform = null;
         _dragApplied = default;
         _edgesSuspended = false;
-        SetEdgesActive(true); // 恢復所有檔案的邊線（被拖檔案的點隨後由 TranslateRoot 更新，期間不會渲染）
+        SetEdgesActive(true);
 
         if (delta.LengthSquared > 1e-12)
         {
-            TranslateRoot(root, delta); // 烘進 B-rep + 網格 + 邊線 + 邊界（量測清空）
-            StatusText = $"已拖曳「{root.Name}」 Δ({delta.X:F2}, {delta.Y:F2}, {delta.Z:F2}) mm（可用 🧩干涉 驗證）";
+            TranslateRoot(root, delta);
+            SetStatus(() => Format("Runtime.Dragged", root.Name, delta.X, delta.Y, delta.Z));
         }
         return true;
     }
diff --git a/src/STPViewer/ViewModels/MainViewModel.Export.cs b/src/STPViewer/ViewModels/MainViewModel.Export.cs
index 279b8c1..e113215 100644
--- a/src/STPViewer/ViewModels/MainViewModel.Export.cs
+++ b/src/STPViewer/ViewModels/MainViewModel.Export.cs
@@ -12,10 +12,11 @@ using CommunityToolkit.Mvvm.Input;
 using Microsoft.Win32;
 using STPViewer.Models;
 using STPViewer.Services;
+using static STPViewer.Services.LocalizationService;
 
 namespace STPViewer.ViewModels;
 
-// ─── 匯出（量測 CSV / 視圖 PNG 截圖 / STEP / STL）────────────────────
+// CSV, STEP, STL, and screenshot export
 public partial class MainViewModel
 {
     [RelayCommand]
@@ -23,32 +24,32 @@ public partial class MainViewModel
     {
         if (Measurements.Count == 0)
         {
-            StatusText = "沒有量測結果可匯出";
+            SetStatus(() => Get("Runtime.CsvEmpty"));
             return;
         }
         var dlg = new SaveFileDialog
         {
-            Title = "匯出量測結果",
-            Filter = "CSV 檔案 (*.csv)|*.csv",
+            Title = Get("Runtime.CsvTitle"),
+            Filter = Get("Runtime.CsvFilter"),
             FileName = $"measurements_{DateTime.Now:yyyyMMdd_HHmmss}.csv",
         };
         if (dlg.ShowDialog() != true) return;
 
         var sb = new StringBuilder();
-        sb.AppendLine("標籤,類型,明細");
+        sb.AppendLine(Get("Runtime.CsvHeader"));
         foreach (MeasurementResult m in Measurements)
         {
             static string Esc(string s) => $"\"{s.Replace("\"", "\"\"")}\"";
-            sb.AppendLine($"{Esc(m.Title)},{m.Kind},{Esc(m.Detail.Replace("\n", " | "))}");
+            sb.AppendLine($"{Esc(m.Title)},{Esc(Get($"Runtime.Kind{m.Kind}"))},{Esc(m.Detail.Replace("\n", " | "))}");
         }
-        File.WriteAllText(dlg.FileName, sb.ToString(), new UTF8Encoding(true)); // BOM：Excel 中文不亂碼
-        StatusText = $"已匯出 {Measurements.Count} 筆量測 → {Path.GetFileName(dlg.FileName)}";
+        File.WriteAllText(dlg.FileName, sb.ToString(), new UTF8Encoding(true)); // BOM for Excel.
+        int count = Measurements.Count;
+        string fileName = Path.GetFileName(dlg.FileName);
+        SetStatus(() => Format("Runtime.CsvExported", count, fileName));
     }
 
     /// <summary>
-    /// 把可見檔案（目前位置，含對齊/旋轉/拖曳結果）匯出成「新的」STEP 檔 —
-    /// 對齊插合後的配合結果可交接給 CAD；不動任何原始檔（唯讀原則不變）。
-    /// 只含 B-rep Solid/Shell（STL 網格、DXF 線架構無法進 STEP B-rep）。
+    /// Exports visible B-rep Solid and Shell objects at their current positions.
     /// </summary>
     [RelayCommand(CanExecute = nameof(IsIdle))]
     private void ExportStepFile()
@@ -60,41 +61,43 @@ public partial class MainViewModel
             .ToList();
         if (geos.Count == 0)
         {
-            StatusText = "沒有可匯出的 B-rep 幾何（STEP 匯出僅含 Solid/Shell；請勾選要匯出的 STEP 檔案）";
+            SetStatus(() => Get("Runtime.StepExportEmpty"));
             return;
         }
 
         var dlg = new SaveFileDialog
         {
-            Title = "匯出目前場景為 STEP（零件在目前對齊位置）",
-            Filter = "STEP 檔案 (*.stp)|*.stp|STEP 檔案 (*.step)|*.step",
+            Title = Get("Runtime.StepExportTitle"),
+            Filter = Get("Runtime.StepExportFilter"),
             FileName = $"assembly_{DateTime.Now:yyyyMMdd_HHmmss}.stp",
         };
         if (dlg.ShowDialog() != true) return;
 
         try
         {
-            // B-rep 已含目前位置（TransformRoot 對 Solid/Shell 整體 Modify）→ 直接寫出
+            // B-rep objects already contain their transformed positions.
             CADability.Project project = CADability.Project.CreateSimpleProject();
             CADability.Model model = project.GetActiveModel();
             foreach (CADability.GeoObject.IGeoObject g in geos) model.Add(g);
             new CADability.ExportStep().WriteToFile(dlg.FileName, project);
-            StatusText = $"已匯出 STEP（{geos.Count} 個實體，目前位置）→ {Path.GetFileName(dlg.FileName)}";
+            int count = geos.Count;
+            string fileName = Path.GetFileName(dlg.FileName);
+            SetStatus(() => Format("Runtime.StepExported", count, fileName));
         }
         catch (Exception ex)
         {
-            StatusText = $"STEP 匯出失敗：{ex.Message}";
+            string error = ex.Message;
+            SetStatus(() => Format("Runtime.StepExportFailed", error));
         }
     }
 
     /// <summary>
-    /// 匯出可見檔案（目前位置）為 STL 網格檔 — 先開參數對話框（範圍/格式/單位/精度 + 三角形數與大小預估）
-    /// 確認後才選路徑寫檔。精細/較粗 = 由 B-rep 重新三角化（背景執行緒）；STL/DXF 來源一律用現有網格。
+    /// Exports visible meshes as STL using the selected format, scale and quality.
     /// </summary>
     [RelayCommand(CanExecute = nameof(IsIdle))]
     private async Task ExportStlFile()
     {
-        // 可匯出 = 可見 leaf 且有網格（DXF 純線架構無網格 → 排除）
+        // Only visible leaves with meshes can be exported.
         var groups = Roots.Where(r => r.IsVisible)
             .Select(r => (Root: r, Leaves: r.Leaves()
                 .Where(l => l.IsVisible && GetMergedMesh(l) is not null).ToList()))
@@ -102,7 +105,7 @@ public partial class MainViewModel
             .ToList();
         if (groups.Count == 0)
         {
-            StatusText = "沒有可匯出的網格（請勾選至少一個含實體網格的檔案）";
+            SetStatus(() => Get("Runtime.StlExportEmpty"));
             return;
         }
 
@@ -110,23 +113,22 @@ public partial class MainViewModel
             .Sum(l => GetMergedMesh(l)!.TriangleIndices.Count / 3L);
         bool hasBrep = groups.SelectMany(g => g.Leaves).Any(l => l.HasBrep && l.SourceGeos.Count > 0);
 
-        // 參數對話框（確認再匯出）
+        // Collect export options.
         var vm = new StlExportViewModel(groups.Count, triangles, hasBrep);
         var dialog = new StlExportDialog(vm) { Owner = Application.Current.MainWindow };
         if (dialog.ShowDialog() != true || vm.Scale is not double scale) return;
 
         var dlg = new SaveFileDialog
         {
-            Title = vm.PerFile ? "匯出 STL（每個檔案各一個，以此為基底檔名）" : "匯出 STL（合併單一檔）",
-            Filter = "STL 檔案 (*.stl)|*.stl",
+            Title = Get(vm.PerFile ? "Runtime.StlExportPerFileTitle" : "Runtime.StlExportMergedTitle"),
+            Filter = Get("Runtime.StlExportFilter"),
             FileName = vm.PerFile
                 ? $"stl_{DateTime.Now:yyyyMMdd_HHmmss}.stl"
                 : $"assembly_{DateTime.Now:yyyyMMdd_HHmmss}.stl",
         };
         if (dlg.ShowDialog() != true) return;
 
-        // UI 執行緒先快照：GeometryModel3D/Model3DGroup 是 DispatcherObject 不可跨執行緒，
-        // 背景只能碰 frozen MeshGeometry3D 與 CADability B-rep（SourceGeos）
+        // Snapshot WPF geometry on the UI thread before background export.
         var snapshot = groups
             .Select(g => (g.Root.Name, Leaves: g.Leaves
                 .Select(l => (Mesh: GetMergedMesh(l)!, l.HasBrep, l.SourceGeos))
@@ -134,9 +136,8 @@ public partial class MainViewModel
             .ToList();
 
         IsBusy = true;
-        StatusText = vm.Quality == StlMeshQuality.Current
-            ? "匯出 STL 中…"
-            : "重新三角化 + 匯出 STL 中…（大組件需要時間）";
+        SetStatus(() => Get(vm.Quality == StlMeshQuality.Current
+            ? "Runtime.StlExporting" : "Runtime.StlRetriangulating"));
         try
         {
             double factor = StlExportService.PrecisionFactor(vm.Quality);
@@ -164,13 +165,16 @@ public partial class MainViewModel
             });
 
             long total = written.Sum(w => (long)w.Triangles);
-            StatusText = written.Count == 1
-                ? $"已匯出 STL（{total:N0} 三角形）→ {Path.GetFileName(written[0].File)}"
-                : $"已匯出 {written.Count} 個 STL（共 {total:N0} 三角形）→ {Path.GetDirectoryName(dlg.FileName)}";
+            int fileCount = written.Count;
+            string destination = fileCount == 1 ? Path.GetFileName(written[0].File) : Path.GetDirectoryName(dlg.FileName)!;
+            SetStatus(() => fileCount == 1
+                ? Format("Runtime.StlExportedOne", total, destination)
+                : Format("Runtime.StlExportedMany", fileCount, total, destination));
         }
         catch (Exception ex)
         {
-            StatusText = $"STL 匯出失敗：{ex.Message}";
+            string error = ex.Message;
+            SetStatus(() => Format("Runtime.StlExportFailed", error));
         }
         finally
         {
@@ -178,16 +182,14 @@ public partial class MainViewModel
         }
     }
 
-    /// <summary>leaf 的合併網格（frozen、未剖切、目前位置）— STL 匯出的「目前顯示網格」來源</summary>
+    /// <summary>Current merged mesh for an exportable leaf.</summary>
     private static MeshGeometry3D? GetMergedMesh(ModelNodeViewModel leaf) =>
         leaf.MergedContent?.Children.Count > 0
             ? (leaf.MergedContent.Children[0] as GeometryModel3D)?.Geometry as MeshGeometry3D
             : null;
 
     /// <summary>
-    /// 收集要寫進 STL 的網格（背景執行緒；輸入是 UI 快照）：
-    /// 精細且有 B-rep → 重新三角化（循序，CADability 非執行緒安全）；
-    /// 其餘（目前網格 / STL 來源）→ 快照的合併網格（frozen，可安全跨執行緒讀取）。
+    /// Selects frozen current meshes or sequentially retessellates B-rep geometry.
     /// </summary>
     private static List<MeshGeometry3D> CollectMeshes(
         IReadOnlyList<(MeshGeometry3D Mesh, bool HasBrep, List<CADability.GeoObject.IGeoObject> SourceGeos)> leaves,
@@ -200,7 +202,7 @@ public partial class MainViewModel
             {
                 List<MeshGeometry3D> tess = StlExportService.Tessellate(sourceGeos, precisionFactor);
                 if (tess.Count > 0) { meshes.AddRange(tess); continue; }
-                // 重新三角化全數失敗 → 退回現有網格，不讓零件憑空消失
+                // Fall back to the current mesh if retessellation yields nothing.
             }
             meshes.Add(mesh);
         }
@@ -221,13 +223,13 @@ public partial class MainViewModel
         if (_viewport is null || _viewport.ActualWidth < 1) return;
         var dlg = new SaveFileDialog
         {
-            Title = "儲存視圖截圖",
-            Filter = "PNG 圖片 (*.png)|*.png",
+            Title = Get("Runtime.ScreenshotTitle"),
+            Filter = Get("Runtime.ScreenshotFilter"),
             FileName = $"stpviewer_{DateTime.Now:yyyyMMdd_HHmmss}.png",
         };
         if (dlg.ShowDialog() != true) return;
 
-        const double scale = 2.0; // 2x 解析度
+        const double scale = 2.0;
         var rtb = new RenderTargetBitmap(
             (int)(_viewport.ActualWidth * scale), (int)(_viewport.ActualHeight * scale),
             96 * scale, 96 * scale, PixelFormats.Pbgra32);
@@ -236,6 +238,7 @@ public partial class MainViewModel
         encoder.Frames.Add(BitmapFrame.Create(rtb));
         using FileStream fs = File.Create(dlg.FileName);
         encoder.Save(fs);
-        StatusText = $"已儲存截圖 → {Path.GetFileName(dlg.FileName)}";
+        string fileName = Path.GetFileName(dlg.FileName);
+        SetStatus(() => Format("Runtime.ScreenshotSaved", fileName));
     }
 }
diff --git a/src/STPViewer/ViewModels/MainViewModel.Gizmo.cs b/src/STPViewer/ViewModels/MainViewModel.Gizmo.cs
index 63df8a9..5ac6a5d 100644
--- a/src/STPViewer/ViewModels/MainViewModel.Gizmo.cs
+++ b/src/STPViewer/ViewModels/MainViewModel.Gizmo.cs
@@ -4,42 +4,41 @@ using System.Windows.Media;
 using System.Windows.Media.Media3D;
 using CommunityToolkit.Mvvm.ComponentModel;
 using HelixToolkit.Wpf;
+using static STPViewer.Services.LocalizationService;
 
 namespace STPViewer.ViewModels;
 
-// ─── Gizmo 三軸操作器（XYZ 箭頭 + 旋轉環；每次放開滑鼠烘進 B-rep）──────
+// Gizmo translation and rotation
 public partial class MainViewModel
 {
     [ObservableProperty]
     private bool gizmoEnabled;
 
     private readonly List<HelixToolkit.Wpf.Manipulator> _gizmoParts = new();
-    private ModelVisual3D? _gizmoProxy;        // 操作器綁定的代理 visual（其 Transform = 使用者拖出的變換）
+    private ModelVisual3D? _gizmoProxy;
     private ModelNodeViewModel? _gizmoTarget;
-    private bool _gizmoDragActive;             // 拖動中（邊線已暫停）
-    private bool _gizmoBaking;                 // 烘焙中，忽略 Transform 變更回呼
-    private bool _gizmoBakePending;            // 已排程烘焙，防同一次放開重複觸發
+    private bool _gizmoDragActive;
+    private bool _gizmoBaking;
+    private bool _gizmoBakePending;
 
-    // 操作器疊圖層：另一個透明 Viewport3D 疊在主視窗上、相機同步、只放操作器 →
-    // 操作器不在主場景，永不被實體遮擋（always-on-top）；空白處滑鼠穿透回主視窗
+    // A synchronized overlay viewport keeps the gizmo above scene geometry.
     private System.Windows.Controls.Viewport3D? _overlayViewport;
-    private ProjectionCamera? _overlayCamera; // 型別跟隨主相機（透視/正交切換，v0.5.0）
+    private ProjectionCamera? _overlayCamera;
 
-    /// <summary>注入操作器疊圖層（透明 Viewport3D，疊在主視窗上、永遠最上層）</summary>
+    /// <summary>Attaches the transparent gizmo overlay viewport.</summary>
     public void AttachOverlay(System.Windows.Controls.Viewport3D overlay)
     {
         _overlayViewport = overlay;
         _overlayCamera = new PerspectiveCamera();
         overlay.Camera = _overlayCamera;
-        // 操作器材質需打光（manipulator 用 DiffuseMaterial）
+        // Manipulator materials need lighting.
         overlay.Children.Add(new ModelVisual3D { Content = new AmbientLight(Color.FromRgb(0x80, 0x80, 0x80)) });
         overlay.Children.Add(new ModelVisual3D { Content = new DirectionalLight(Colors.White, new Vector3D(-1, -1, -3)) });
         SyncOverlayCamera();
     }
 
     /// <summary>
-    /// 疊圖層相機跟隨主相機（每次主相機變更時呼叫，讓操作器疊在正確螢幕位置）。
-    /// 主相機可能在透視/正交間切換（Orthographic 屬性）→ 疊圖層相機「型別」也要跟著換，投影才一致。
+    /// Keeps the overlay camera in sync with the main camera and projection mode.
     /// </summary>
     private void SyncOverlayCamera()
     {
@@ -78,7 +77,7 @@ public partial class MainViewModel
 
     partial void OnSelectedNodeChanged(ModelNodeViewModel? value)
     {
-        if (GizmoEnabled) UpdateGizmo(); // 換選取 → 操作器跟著換目標
+        if (GizmoEnabled) UpdateGizmo();
     }
 
     private void UpdateGizmo()
@@ -90,12 +89,12 @@ public partial class MainViewModel
             : Roots.Count == 1 ? Roots[0] : null;
         if (root is null || root.Bounds.IsEmpty)
         {
-            StatusText = "操作器：請先在樹面板點選要操作的檔案";
+            SetStatus(() => Get("Runtime.GizmoSelectFile"));
             GizmoEnabled = false;
             return;
         }
         _gizmoTarget = root;
-        SyncOverlayCamera(); // 操作器出現前先對齊相機
+        SyncOverlayCamera();
 
         Rect3D b = root.Bounds;
         var center = new Point3D(b.X + b.SizeX / 2, b.Y + b.SizeY / 2, b.Z + b.SizeZ / 2);
@@ -112,18 +111,18 @@ public partial class MainViewModel
             man.Position = center;
             man.Bind(_gizmoProxy);
             _gizmoParts.Add(man);
-            _overlayViewport!.Children.Add(man); // 放疊圖層 → 永不被實體遮擋
+            _overlayViewport!.Children.Add(man);
         }
-        // 平移箭頭（X 紅 / Y 綠 / Z 藍 — 業界慣例）
+        // Translation arrows: X red, Y green, Z blue.
         AddPart(new TranslateManipulator { Direction = new Vector3D(1, 0, 0), Color = Colors.Red,   Length = diag * 0.22, Diameter = diag * 0.016 });
         AddPart(new TranslateManipulator { Direction = new Vector3D(0, 1, 0), Color = Colors.Green, Length = diag * 0.22, Diameter = diag * 0.016 });
         AddPart(new TranslateManipulator { Direction = new Vector3D(0, 0, 1), Color = Colors.Blue,  Length = diag * 0.22, Diameter = diag * 0.016 });
-        // 旋轉環
+        // Rotation rings
         AddPart(new RotateManipulator { Axis = new Vector3D(1, 0, 0), Color = Colors.Red,   Diameter = diag * 0.34, InnerDiameter = diag * 0.30, Length = diag * 0.012 });
         AddPart(new RotateManipulator { Axis = new Vector3D(0, 1, 0), Color = Colors.Green, Diameter = diag * 0.34, InnerDiameter = diag * 0.30, Length = diag * 0.012 });
         AddPart(new RotateManipulator { Axis = new Vector3D(0, 0, 1), Color = Colors.Blue,  Diameter = diag * 0.34, InnerDiameter = diag * 0.30, Length = diag * 0.012 });
 
-        StatusText = $"操作器：拖箭頭沿軸移動「{root.Name}」、拖環繞軸旋轉；放開即定位";
+        SetStatus(() => Format("Runtime.GizmoHint", root.Name));
     }
 
     private void RemoveGizmo()
@@ -143,7 +142,7 @@ public partial class MainViewModel
         _gizmoParts.Clear();
         _gizmoProxy = null;
 
-        if (_gizmoTarget is not null) // 清掉殘留的暫時 Transform（用 Identity，不可 null → 否則 FindHits crash）
+        if (_gizmoTarget is not null)
             foreach (ModelNodeViewModel l in _gizmoTarget.Leaves())
                 if (l.BodyVisual is not null)
                     l.BodyVisual.Transform = Transform3D.Identity;
@@ -156,7 +155,7 @@ public partial class MainViewModel
         }
     }
 
-    /// <summary>操作器拖動中：把代理的 Transform 套到目標檔案的所有 BodyVisual（暫時、GPU 端）</summary>
+    /// <summary>Applies the proxy transform to target visuals during dragging.</summary>
     private void GizmoTransformChanged(object? sender, EventArgs e)
     {
         if (_gizmoBaking || _gizmoTarget is null || _gizmoProxy is null) return;
@@ -165,21 +164,21 @@ public partial class MainViewModel
         {
             _gizmoDragActive = true;
             _edgesSuspended = true;
-            SetEdgesActive(false); // 邊線逐幀重建會卡，拖動中暫停
+            SetEdgesActive(false);
         }
         foreach (ModelNodeViewModel l in _gizmoTarget.Leaves())
             if (l.BodyVisual is not null)
                 l.BodyVisual.Transform = t;
     }
 
-    /// <summary>滑鼠放開（MainWindow 轉發，handledEventsToo）：把累積變換烘進 B-rep 並重置操作器</summary>
+    /// <summary>Commits the accumulated transform and resets the gizmo on mouse release.</summary>
     public void OnGizmoMouseUp()
     {
         if (_gizmoTarget is null || _gizmoProxy is null || _gizmoBakePending) return;
         Matrix3D m = _gizmoProxy.Transform?.Value ?? Matrix3D.Identity;
-        if (m.IsIdentity) return; // 只是點一下、沒拖操作器 → 不烘焙
+        if (m.IsIdentity) return;
 
-        // 延後到 manipulator 自身的 mouse-up 處理（釋放捕捉等）完成後再烘焙，避免在其事件中改動視覺樹造成 reentrancy
+        // Commit after the manipulator completes its mouse-up handling.
         _gizmoBakePending = true;
         _viewport?.Dispatcher.BeginInvoke(new Action(() => BakeGizmo(m)),
             System.Windows.Threading.DispatcherPriority.Background);
@@ -191,19 +190,19 @@ public partial class MainViewModel
         if (_gizmoTarget is null) return;
         ModelNodeViewModel root = _gizmoTarget;
 
-        _gizmoBaking = true; // 防 proxy 歸零觸發 GizmoTransformChanged 重入
+        _gizmoBaking = true;
         foreach (ModelNodeViewModel l in root.Leaves())
             if (l.BodyVisual is not null)
-                l.BodyVisual.Transform = Transform3D.Identity; // 清暫時位移（用 Identity，不可 null）
-        if (_gizmoProxy is not null) _gizmoProxy.Transform = Transform3D.Identity; // 綁定 → 操作器歸零
+                l.BodyVisual.Transform = Transform3D.Identity;
+        if (_gizmoProxy is not null) _gizmoProxy.Transform = Transform3D.Identity;
         _gizmoBaking = false;
         _gizmoDragActive = false;
         _edgesSuspended = false;
         SetEdgesActive(true);
 
-        TransformRoot(root, Services.RigidAlign.ToModOp(m), m); // 烘進 B-rep（量測精度不受影響）
+        TransformRoot(root, Services.RigidAlign.ToModOp(m), m);
 
-        // 操作器移到變換後的新中心
+        // Move the gizmo to the transformed center.
         Rect3D b = root.Bounds;
         if (!b.IsEmpty)
         {
@@ -211,6 +210,6 @@ public partial class MainViewModel
             foreach (HelixToolkit.Wpf.Manipulator man in _gizmoParts)
                 man.Position = center;
         }
-        StatusText = $"已套用操作器變換「{root.Name}」（可用 🧩干涉 驗證）";
+        SetStatus(() => Format("Runtime.GizmoApplied", root.Name));
     }
 }
diff --git a/src/STPViewer/ViewModels/MainViewModel.Interference.cs b/src/STPViewer/ViewModels/MainViewModel.Interference.cs
index 24b8a67..a49a2ca 100644
--- a/src/STPViewer/ViewModels/MainViewModel.Interference.cs
+++ b/src/STPViewer/ViewModels/MainViewModel.Interference.cs
@@ -9,10 +9,11 @@ using CommunityToolkit.Mvvm.Input;
 using HelixToolkit.Wpf;
 using STPViewer.Models;
 using STPViewer.Services;
+using static STPViewer.Services.LocalizationService;
 
 namespace STPViewer.ViewModels;
 
-// ─── 干涉檢查 ────────────────────────────────────────────────────────
+// Interference checking
 public partial class MainViewModel
 {
     [RelayCommand(CanExecute = nameof(IsIdle))]
@@ -22,7 +23,8 @@ public partial class MainViewModel
         var visibleRoots = Roots.Where(r => r.IsVisible).ToList();
         if (visibleRoots.Count < 2)
         {
-            StatusText = $"干涉檢查需要至少 2 個可見檔案（目前 {visibleRoots.Count} 個）— 用樹面板勾選";
+            int visibleCount = visibleRoots.Count;
+            SetStatus(() => Format("Runtime.InterferenceNeedTwo", visibleCount));
             return;
         }
 
@@ -33,7 +35,7 @@ public partial class MainViewModel
                 .Select(m => _faceMap[(GeometryModel3D)m].Mesh)
                 .ToList();
 
-        // 網格快照（開跑後零件被改走也不會半途換料；v0.4.0 起運算期間指令已鎖，這裡是雙保險）
+        // Snapshot meshes before background calculations.
         var meshes = visibleRoots.ToDictionary(r => r, MeshesOf);
 
         IsBusy = true;
@@ -45,7 +47,8 @@ public partial class MainViewModel
                 {
                     pairs++;
                     string nameA = visibleRoots[i].Name, nameB = visibleRoots[j].Name;
-                    StatusText = $"干涉檢查中（第 {pairs} 組）：{nameA} ⟷ {nameB} …";
+                    int currentPair = pairs;
+                    SetStatus(() => Format("Runtime.InterferenceChecking", currentPair, nameA, nameB));
                     var a = meshes[visibleRoots[i]];
                     var b = meshes[visibleRoots[j]];
                     InterferenceResult result = await Task.Run(() => InterferenceService.Check(a, b));
@@ -53,11 +56,15 @@ public partial class MainViewModel
                     if (result.Intersects) intersecting++;
                 }
             if (pairs > 1)
-                StatusText = $"干涉檢查完成：{pairs} 組配對、{intersecting} 組相交";
+            {
+                int checkedPairs = pairs, hits = intersecting;
+                SetStatus(() => Format("Runtime.InterferenceCompleted", checkedPairs, hits));
+            }
         }
         catch (Exception ex)
         {
-            StatusText = $"干涉檢查失敗：{ex.Message}";
+            string error = ex.Message;
+            SetStatus(() => Format("Runtime.InterferenceFailed", error));
         }
         finally
         {
@@ -78,9 +85,8 @@ public partial class MainViewModel
             m = new MeasurementResult
             {
                 Kind = MeasureMode.Interference,
-                TitleFor = _ => $"🧩 干涉！{nameA} ⟷ {nameB}",
-                DetailFor = _ => $"兩零件相交（不 match）\n相交三角形對 = {pairs:N0}\n" +
-                                 $"紅色線 = 干涉交線（{segCount:N0} 段）\n（共面貼合不會被算為干涉）",
+                TitleFor = _ => Format("Runtime.InterferenceHitTitle", nameA, nameB),
+                DetailFor = _ => Format("Runtime.InterferenceHitDetail", pairs, segCount),
             };
             var pts = new Point3DCollection(Math.Min(result.Segments.Count, 20000) * 2);
             foreach ((Point3D s0, Point3D s1) in result.Segments) { pts.Add(s0); pts.Add(s1); }
@@ -88,15 +94,17 @@ public partial class MainViewModel
             if (result.Segments.Count > 0)
             {
                 Point3D at = result.Segments[0].A;
-                m.Overlays.Add(new BillboardTextVisual3D
+                var label = new BillboardTextVisual3D
                 {
                     Position = at + new Vector3D(0, 0, markerR * 3),
-                    Text = "干涉",
+                    Text = Get("Runtime.InterferenceLabel"),
                     Foreground = Brushes.White,
                     Background = Brushes.Red,
                     Padding = new Thickness(5, 2, 5, 2),
                     FontSize = 14,
-                });
+                };
+                m.Overlays.Add(label);
+                m.DynamicLabels.Add((label, _ => Get("Runtime.InterferenceLabel")));
             }
         }
         else
@@ -107,9 +115,8 @@ public partial class MainViewModel
             m = new MeasurementResult
             {
                 Kind = MeasureMode.Interference,
-                TitleFor = u => $"🧩 無干涉  gap ≈ {Units.L(gap, u)}",
-                DetailFor = u => $"{nameA} ⟷ {nameB} 無相交\n最小間隙 ≈ {Units.L(gap, u)}（網格近似）\n" +
-                                 $"gap ≈ 0 即為貼合（match）\n點 1 {Units.P(ga, u)}\n點 2 {Units.P(gb, u)}",
+                TitleFor = u => Format("Runtime.InterferenceClearTitle", Units.L(gap, u)),
+                DetailFor = u => Format("Runtime.InterferenceClearDetail", nameA, nameB, Units.L(gap, u), Units.P(ga, u), Units.P(gb, u)),
             };
             m.Overlays.Add(new SphereVisual3D { Center = ga, Radius = markerR, Fill = Brushes.OrangeRed });
             m.Overlays.Add(new SphereVisual3D { Center = gb, Radius = markerR, Fill = Brushes.OrangeRed });
@@ -122,14 +129,14 @@ public partial class MainViewModel
             var label = new BillboardTextVisual3D
             {
                 Position = ga + d / 2 + new Vector3D(0, 0, markerR * 2),
-                Text = $"gap {Units.L(gap, UnitSystem.Millimeter)}",
+                Text = Format("Runtime.GapLabel", Units.L(gap, UnitSystem.Millimeter)),
                 Foreground = Brushes.Black,
                 Background = new SolidColorBrush(Color.FromArgb(200, 255, 255, 210)),
                 Padding = new Thickness(4, 2, 4, 2),
                 FontSize = 14,
             };
             m.Overlays.Add(label);
-            m.DynamicLabels.Add((label, u => $"gap {Units.L(gap, u)}"));
+            m.DynamicLabels.Add((label, u => Format("Runtime.GapLabel", Units.L(gap, u))));
         }
         AddMeasurement(m);
     }
diff --git a/src/STPViewer/ViewModels/MainViewModel.Localization.cs b/src/STPViewer/ViewModels/MainViewModel.Localization.cs
new file mode 100644
index 0000000..af90cfb
--- /dev/null
+++ b/src/STPViewer/ViewModels/MainViewModel.Localization.cs
@@ -0,0 +1,32 @@
+using CommunityToolkit.Mvvm.Input;
+using STPViewer.Models;
+using STPViewer.Services;
+
+namespace STPViewer.ViewModels;
+
+public partial class MainViewModel
+{
+    public string SelectedLanguage
+    {
+        get => LocalizationService.Instance.Language;
+        set => LocalizationService.Instance.SetLanguage(value);
+    }
+
+    public IReadOnlyList<LanguageDefinition> Languages => LocalizationService.Instance.Languages;
+
+    public void InitializeLocalization() =>
+        LocalizationService.Instance.LanguageChanged += OnLanguageChanged;
+
+    public void DisposeLocalization() =>
+        LocalizationService.Instance.LanguageChanged -= OnLanguageChanged;
+
+    [RelayCommand]
+    private void ChangeLanguage(string language) => SelectedLanguage = language;
+
+    private void OnLanguageChanged(object? sender, EventArgs e)
+    {
+        OnPropertyChanged(nameof(SelectedLanguage));
+        QuickBar.RefreshText();
+        RefreshLocalizedText();
+    }
+}
diff --git a/src/STPViewer/ViewModels/MainViewModel.Section.cs b/src/STPViewer/ViewModels/MainViewModel.Section.cs
index 5b960f2..618cecd 100644
--- a/src/STPViewer/ViewModels/MainViewModel.Section.cs
+++ b/src/STPViewer/ViewModels/MainViewModel.Section.cs
@@ -9,19 +9,19 @@ using CommunityToolkit.Mvvm.Input;
 using HelixToolkit.Wpf;
 using STPViewer.Models;
 using STPViewer.Services;
+using static STPViewer.Services.LocalizationService;
 
 namespace STPViewer.ViewModels;
 
-// ─── 剖面（CPU 網格裁切；v0.4.0 起裁切在背景執行緒平行計算，UI 不凍結）──
+// Section clipping
 public partial class MainViewModel
 {
     private readonly DispatcherTimer _sectionTimer;
     private RectangleVisual3D? _sectionPlaneVisual;
-    private Point3D _sectionPlanePoint;   // SectionEnabled 時的剖切平面（合併邊線重建用）
+    private Point3D _sectionPlanePoint;
     private Vector3D _sectionNormal;
 
-    // 背景裁切 guard：進行中又有新變更（拉滑桿/換軸/零件平移）→ 完成後用最新參數重跑一輪。
-    // 不要改回同步呼叫 ClipMesh —— 大檔（64k 面）整場景裁切會凍結 UI 數秒
+    // Reapply clipping if parameters change while background work is running.
     private bool _sectionApplying;
     private bool _sectionReapply;
 
@@ -32,20 +32,20 @@ public partial class MainViewModel
     [ObservableProperty]
     private int sectionAxisIndex;
 
-    /// <summary>剖面位置（沿軸 0~100%）</summary>
+    /// <summary>Section position along the selected axis, from 0 to 100%.</summary>
     [ObservableProperty]
     private double sectionPosition = 50;
 
     [ObservableProperty]
     private bool sectionFlip;
 
-    /// <summary>剖面參數列的「✕ 關閉」按鈕（參數列只在剖面開啟時顯示）</summary>
+    /// <summary>Closes the section parameter bar.</summary>
     [RelayCommand]
     private void CloseSection() => SectionEnabled = false;
 
-    // ── 3點自訂剖切平面（SectionAxisIndex == 3，v0.5.0）──
+    // Three-point custom cutting plane
     private const int CustomAxisIndex = 3;
-    private Vector3D? _customNormal;                                  // null = 尚未定義（等使用者點 3 點）
+    private Vector3D? _customNormal;
     private readonly List<Point3D> _sectionPicks = new();
     private readonly List<Visual3D> _sectionPickOverlays = new();
 
@@ -60,11 +60,11 @@ public partial class MainViewModel
         if (value == CustomAxisIndex)
         {
             if (_customNormal is null)
-                StatusText = "3點剖面：請在模型上點 3 個點定義剖切平面（Esc 取消）";
+                SetStatus(() => Get("Runtime.SectionPickPrompt"));
         }
         else
         {
-            // 離開自訂平面 → 丟棄舊平面（再選「3點」即重新定義）
+            // Leaving custom mode discards the old plane.
             _customNormal = null;
             ClearSectionPicks();
         }
@@ -73,14 +73,14 @@ public partial class MainViewModel
 
     partial void OnSectionPositionChanged(double value)
     {
-        if (value < 0) { SectionPosition = 0; return; }   // 位置數值輸入框防呆
+        if (value < 0) { SectionPosition = 0; return; }
         if (value > 100) { SectionPosition = 100; return; }
         ScheduleSection();
     }
 
     partial void OnSectionFlipChanged(bool value) => ScheduleSection();
 
-    /// <summary>3點剖面定義模式中的點擊（OnViewportClick 轉入）。回傳 true = 已消費此點擊。</summary>
+    /// <summary>Handles a custom plane pick; returns true when the click is consumed.</summary>
     public bool HandleSectionPlanePick(System.Windows.Point position)
     {
         if (!SectionEnabled || SectionAxisIndex != CustomAxisIndex || _customNormal is not null) return false;
@@ -98,13 +98,14 @@ public partial class MainViewModel
         }
         if (hit is null)
         {
-            StatusText = $"3點剖面：未命中模型表面（已選 {_sectionPicks.Count}/3 點，Esc 取消）";
+            int selected = _sectionPicks.Count;
+            SetStatus(() => Format("Runtime.SectionNoHit", selected));
             return true;
         }
         if (_sectionPicks.Count == 2 &&
             Vector3D.CrossProduct(_sectionPicks[1] - _sectionPicks[0], hit.Value - _sectionPicks[0]).LengthSquared < 1e-12)
         {
-            StatusText = "3點剖面：三點共線，請改選不共線的第 3 點";
+            SetStatus(() => Get("Runtime.SectionCollinear"));
             return true;
         }
 
@@ -116,7 +117,8 @@ public partial class MainViewModel
 
         if (_sectionPicks.Count < 3)
         {
-            StatusText = $"3點剖面：已選 {_sectionPicks.Count}/3 點";
+            int selected = _sectionPicks.Count;
+            SetStatus(() => Format("Runtime.SectionPicked", selected));
             return true;
         }
 
@@ -124,25 +126,25 @@ public partial class MainViewModel
         ClearSectionPicks();
         if (n.LengthSquared < 1e-12)
         {
-            StatusText = "3點剖面：三點退化（共線），請重新點選";
+            SetStatus(() => Get("Runtime.SectionDegenerate"));
             return true;
         }
         n.Normalize();
         _customNormal = n;
-        StatusText = $"3點剖面：平面已定義（法向 {n.X:F2}, {n.Y:F2}, {n.Z:F2}）— 用位置滑桿掃剖面";
+        SetStatus(() => Format("Runtime.SectionDefined", n.X, n.Y, n.Z));
         ApplySection();
         return true;
     }
 
-    /// <summary>取消 3 點平面定義（Esc / 關剖面）。回傳 true = 有取消動作。</summary>
+    /// <summary>Cancels custom plane picking; returns true if it was active.</summary>
     private bool CancelSectionPickIfActive(bool quiet = false)
     {
         bool picking = SectionEnabled && SectionAxisIndex == CustomAxisIndex && _customNormal is null;
         if (_sectionPicks.Count == 0 && !picking) return false;
         ClearSectionPicks();
         if (SectionAxisIndex == CustomAxisIndex && _customNormal is null)
-            SectionAxisIndex = 0; // 回 X 軸
-        if (!quiet) StatusText = "已取消 3 點剖面定義";
+            SectionAxisIndex = 0;
+        if (!quiet) SetStatus(() => Get("Runtime.SectionCancelled"));
         return true;
     }
 
@@ -165,8 +167,7 @@ public partial class MainViewModel
 
         if (!SectionEnabled)
         {
-            // 還原原始幾何（換回 fi.Mesh 參照，便宜、同步即可）。
-            // 若背景裁切還在跑，其 await 之後會看到 SectionEnabled=false 而放棄套用
+            // Restore original meshes. Background clipping checks SectionEnabled before applying.
             foreach ((Model3D model, FaceInfo fi) in _faceMap)
                 if (model is GeometryModel3D gm && !ReferenceEquals(gm.Geometry, fi.Mesh))
                     gm.Geometry = fi.Mesh;
@@ -176,8 +177,8 @@ public partial class MainViewModel
                 _viewport.Children.Remove(_sectionPlaneVisual);
                 _sectionPlaneVisual = null;
             }
-            ApplyRenderMode(); // 剖面關閉 → 瀏覽模式可切回合併網格
-            StatusText = "剖面已關閉";
+            ApplyRenderMode();
+            SetStatus(() => Get("Runtime.SectionClosed"));
             return;
         }
 
@@ -195,7 +196,7 @@ public partial class MainViewModel
                 Vector3D axis;
                 if (SectionAxisIndex == CustomAxisIndex)
                 {
-                    if (_customNormal is null) return; // 平面尚未定義（等使用者點 3 點）
+                    if (_customNormal is null) return;
                     axis = _customNormal.Value;
                 }
                 else
@@ -211,8 +212,7 @@ public partial class MainViewModel
                 Point3D min = bounds.Location;
                 var size = new Vector3D(bounds.SizeX, bounds.SizeY, bounds.SizeZ);
                 Point3D center = min + size / 2;
-                // 平面位置：場景 AABB 8 個角投影到法向的 [dmin, dmax]，滑桿 t 內插
-                //（軸向法向 = 與舊版逐軸計算等價；任意法向也成立）
+                // Interpolate along the projected bounds of the scene AABB.
                 double dmin = double.MaxValue, dmax = double.MinValue;
                 for (int ci = 0; ci < 8; ci++)
                 {
@@ -228,9 +228,7 @@ public partial class MainViewModel
                 Point3D planePoint = center + axis * (dStar - Vector3D.DotProduct((Vector3D)center, axis));
                 Vector3D normal = SectionFlip ? -axis : axis;
 
-                // UI 執行緒快照（原始 mesh 皆已 Freeze，可跨執行緒），背景平行裁切，回 UI 一次換上。
-                // 裁切期間若參數又變 / 零件被平移（TransformRoot 會呼叫 ApplySection）→
-                // _sectionReapply 讓迴圈用最新的 fi.Mesh 與平面重跑，最終狀態必為最新
+                // Clip frozen meshes in the background, then apply on the UI thread.
                 var models = new List<GeometryModel3D>(_faceMap.Count);
                 var sources = new List<MeshGeometry3D>(_faceMap.Count);
                 foreach ((Model3D model, FaceInfo fi) in _faceMap)
@@ -248,19 +246,23 @@ public partial class MainViewModel
                     return result;
                 });
 
-                if (!SectionEnabled) return; // 裁切期間被關掉 → 還原分支已處理，丟棄結果
+                if (!SectionEnabled) return;
 
                 for (int i = 0; i < models.Count; i++)
-                    models[i].Geometry = clipped[i]; // 已移除檔案的殘留 model 賦值無害（不在視覺樹上）
+                    models[i].Geometry = clipped[i];
 
                 _sectionPlanePoint = planePoint;
                 _sectionNormal = normal;
                 foreach (ModelNodeViewModel root in Roots) RefreshRootEdges(root);
 
-                ApplyRenderMode(); // 剖面開啟 → 改用逐面（裁切後幾何）
+                ApplyRenderMode();
                 UpdateSectionPlaneVisual(planePoint, axis, size);
-                string axisName = SectionAxisIndex == CustomAxisIndex ? "自訂平面" : $"{"XYZ"[SectionAxisIndex]} 軸";
-                StatusText = $"剖面：{axisName} {SectionPosition:F0}%" + (SectionFlip ? "（反向）" : "");
+                int axisIndex = SectionAxisIndex;
+                double position = SectionPosition;
+                bool flip = SectionFlip;
+                SetStatus(() => Format("Runtime.SectionStatus",
+                    axisIndex == CustomAxisIndex ? Get("Runtime.CustomPlane") : Format("Runtime.Axis", "XYZ"[axisIndex]),
+                    position, flip ? Get("Runtime.Reversed") : ""));
             } while (_sectionReapply);
         }
         finally
@@ -279,7 +281,7 @@ public partial class MainViewModel
             0 => (new Vector3D(0, 1, 0), size.Y, size.Z),
             1 => (new Vector3D(1, 0, 0), size.X, size.Z),
             2 => (new Vector3D(1, 0, 0), size.X, size.Y),
-            _ => (AnyPerpendicular(axis), size.Length * 0.8, size.Length * 0.8), // 自訂平面
+            _ => (AnyPerpendicular(axis), size.Length * 0.8, size.Length * 0.8),
         };
         lenDir.Normalize();
         _sectionPlaneVisual = new RectangleVisual3D
@@ -294,7 +296,7 @@ public partial class MainViewModel
         _viewport!.Children.Add(_sectionPlaneVisual);
     }
 
-    /// <summary>取任一與 n 垂直的單位向量（自訂平面的指示矩形方向用）</summary>
+    /// <summary>Returns a unit vector perpendicular to n for the custom plane visual.</summary>
     private static Vector3D AnyPerpendicular(Vector3D n)
     {
         Vector3D v = Math.Abs(n.Z) < 0.9
diff --git a/src/STPViewer/ViewModels/MainViewModel.cs b/src/STPViewer/ViewModels/MainViewModel.cs
index 2883c8a..0a53617 100644
--- a/src/STPViewer/ViewModels/MainViewModel.cs
+++ b/src/STPViewer/ViewModels/MainViewModel.cs
@@ -14,6 +14,7 @@ using HelixToolkit.Wpf;
 using Microsoft.Win32;
 using STPViewer.Models;
 using STPViewer.Services;
+using static STPViewer.Services.LocalizationService;
 
 namespace STPViewer.ViewModels;
 
@@ -22,34 +23,33 @@ public partial class MainViewModel : ObservableObject
     private readonly StepImportService _importService = new();
     private readonly MeasurementService _measureService = new();
 
-    /// <summary>渲染物件 → B-rep Face 反查表（HitTest 用；overlay 不在表內所以自然被忽略）</summary>
+    /// <summary>Maps rendered face models to their B-rep face data for hit testing.</summary>
     private readonly Dictionary<Model3D, FaceInfo> _faceMap = new();
 
-    /// <summary>合併網格 → leaf 反查表（拖曳模式在瀏覽渲染下 hit-test 用）</summary>
+    /// <summary>Maps merged meshes to leaves for drag hit testing.</summary>
     private readonly Dictionary<Model3D, ModelNodeViewModel> _mergedMap = new();
 
-    /// <summary>合併網格 → (每面頂點起始邊界, 對應 FaceInfo)。命中合併網格時用三角形頂點 index 二分搜尋反查回是哪個面，
-    /// 讓量測模式也能 render 合併網格（62 個 model）而非逐面（數萬個 model）。starts 長度 = faces+1，最後一格為總頂點數。
-    /// 邊界由匯入時依面序串接而成，與 BuildMergedMesh 串接順序一致；平移不改各面頂點數，故邊界永久有效。</summary>
+    /// <summary>Vertex boundaries and faces used to resolve hits on merged meshes.
+    /// The order matches BuildMergedMesh; transforms do not change vertex counts.</summary>
     private readonly Dictionary<Model3D, (int[] Starts, FaceInfo[] Faces)> _mergedFaceRanges = new();
 
     private HelixViewport3D? _viewport;
     private int _paletteIndex;
     private readonly Dictionary<MeasureMode, int> _counters = new();
 
-    // 兩段式量測的第一次拾取暫存
-    private Point3D? _pendingPoint;          // 距離
-    private DirectionPick? _pendingDirection; // 角度
-    private FaceInfo? _pendingFace;           // 面距
-    private (ModelNodeViewModel Root, Point3D Point)? _pendingAlign; // 兩點對齊
-    private readonly List<(ModelNodeViewModel Root, Point3D P)> _align3 = new(); // 三點對齊（前3=來源、後3=目標）
+    // First picks for multi-step measurements.
+    private Point3D? _pendingPoint;
+    private DirectionPick? _pendingDirection;
+    private FaceInfo? _pendingFace;
+    private (ModelNodeViewModel Root, Point3D Point)? _pendingAlign;
+    private readonly List<(ModelNodeViewModel Root, Point3D P)> _align3 = new();
     private readonly List<Visual3D> _pendingOverlays = new();
 
-    /// <summary>樹面板目前選取的節點（MainWindow SelectedItemChanged 轉發；旋轉指令的目標）</summary>
+    /// <summary>Selected tree node used as the target for commands.</summary>
     [ObservableProperty]
     private ModelNodeViewModel? selectedNode;
 
-    // 互動中暫停邊線：轉動/縮放/平移時隱藏 LinesVisual3D，停下再顯示 → 大組件流暢
+    // Suspend edge rendering during camera interaction.
     private readonly DispatcherTimer _interactionTimer;
     private bool _edgesSuspended;
 
@@ -57,7 +57,24 @@ public partial class MainViewModel : ObservableObject
     private MeasureMode currentMode = MeasureMode.None;
 
     [ObservableProperty]
-    private string statusText = "就緒 — 匯入 STP/STEP/STL/DXF（拖放亦可）。右鍵旋轉、滾輪縮放、中鍵或 Shift+左鍵平移";
+    private string statusText = Get("Runtime.Ready");
+
+    private Func<string> _statusTextFor = () => Get("Runtime.Ready");
+
+    private void SetStatus(Func<string> textFor)
+    {
+        _statusTextFor = textFor;
+        StatusText = textFor();
+    }
+
+    public void RefreshLocalizedText()
+    {
+        foreach (MeasurementResult result in Measurements) result.RefreshText();
+        foreach (ModelNodeViewModel root in Roots) root.RefreshLocalizedText();
+        if (!string.IsNullOrWhiteSpace(TreeFilter))
+            foreach (ModelNodeViewModel root in Roots) root.ApplyFilter(TreeFilter);
+        StatusText = _statusTextFor();
+    }
 
     [ObservableProperty]
     [NotifyCanExecuteChangedFor(nameof(ImportCommand))]
@@ -71,7 +88,7 @@ public partial class MainViewModel : ObservableObject
     [ObservableProperty]
     private bool useInch;
 
-    /// <summary>樹面板名稱過濾字串（只影響樹顯示，不影響 3D 可見性）</summary>
+    /// <summary>Tree name filter; does not affect viewport visibility.</summary>
     [ObservableProperty]
     private string? treeFilter;
 
@@ -80,16 +97,16 @@ public partial class MainViewModel : ObservableObject
         foreach (ModelNodeViewModel root in Roots) root.ApplyFilter(value);
     }
 
-    /// <summary>最近開啟檔案（MRU，最多 10 筆；隨 settings.json 保存）</summary>
+    /// <summary>Recently opened files saved in settings.json.</summary>
     public ObservableCollection<string> RecentFiles { get; } = new();
 
     public ObservableCollection<ModelNodeViewModel> Roots { get; } = new();
     public ObservableCollection<MeasurementResult> Measurements { get; } = new();
 
-    /// <summary>快速工具列自訂（選單列有全部功能，快速列只放勾選的常用按鈕）</summary>
+    /// <summary>Quick bar button selections.</summary>
     public QuickBarViewModel QuickBar { get; } = new();
 
-    // ─── 使用者設定（視窗由 MainWindow 處理；VM 管單位 + MRU）─────
+    // User settings
 
     public void LoadSettings(AppSettings s)
     {
@@ -103,6 +120,7 @@ public partial class MainViewModel : ObservableObject
     public void SaveSettingsInto(AppSettings s)
     {
         s.UseInch = UseInch;
+        s.Language = SelectedLanguage;
         s.RecentFiles = RecentFiles.ToList();
         s.QuickBarKeys = QuickBar.ToKeys();
     }
@@ -121,23 +139,18 @@ public partial class MainViewModel : ObservableObject
         _sectionTimer = new DispatcherTimer { Interval = TimeSpan.FromMilliseconds(100) };
         _sectionTimer.Tick += (_, _) => { _sectionTimer.Stop(); ApplySection(); };
 
-        // 相機停止移動 180ms 後恢復邊線
+        // Restore edges after camera movement stops.
         _interactionTimer = new DispatcherTimer { Interval = TimeSpan.FromMilliseconds(180) };
         _interactionTimer.Tick += (_, _) => { _interactionTimer.Stop(); ResumeEdges(); };
     }
 
     private UnitSystem CurrentUnit => UseInch ? UnitSystem.Inch : UnitSystem.Millimeter;
 
-    /// <summary>由 MainWindow 注入 viewport（桌面工具，不做過度抽象）</summary>
+    /// <summary>Attaches the viewport from MainWindow.</summary>
     public void Attach(HelixViewport3D viewport)
     {
         _viewport = viewport;
-        // 相機一動就暫停邊線/逐面（轉動/縮放/平移皆觸發），停下 180ms 再恢復。
-        // 兩個事件都訂閱，互補保底：
-        //   1) viewport.CameraChanged（控制項層級 routed event）— 相機實例若被 Helix 內部換掉也接得住；
-        //   2) Camera.Changed（Freezable，相機 Position/方向一被改就觸發）— 確保每次移動都收到。
-        // 舊寫法只訂 Camera.Changed 且包在 null 檢查裡，萬一相機實例被換就永久失聯 → 暫停機制全失效。
-        // 重複觸發 OnCameraMoved 無害（idempotent，內部有 _edgesSuspended guard）。
+        // The viewport event also catches camera instance replacements by HelixToolkit.
         viewport.CameraChanged += (_, _) => OnCameraMoved();
         if (viewport.Camera is not null)
             viewport.Camera.Changed += (_, _) => OnCameraMoved();
@@ -145,7 +158,7 @@ public partial class MainViewModel : ObservableObject
 
     private void OnCameraMoved()
     {
-        SyncOverlayCamera(); // 操作器疊圖層跟著主相機
+        SyncOverlayCamera();
         if (!_edgesSuspended) { _edgesSuspended = true; SetEdgesActive(false); }
         _interactionTimer.Stop();
         _interactionTimer.Start();
@@ -157,7 +170,7 @@ public partial class MainViewModel : ObservableObject
         SetEdgesActive(true);
     }
 
-    /// <summary>只切換 root 合併邊線的 viewport 掛載（不重建 Points）</summary>
+    /// <summary>Shows or hides merged root edges without rebuilding points.</summary>
     private void SetEdgesActive(bool active)
     {
         if (_viewport is null) return;
@@ -166,47 +179,45 @@ public partial class MainViewModel : ObservableObject
                 SyncVisual(root.EdgeVisual, active && root.EdgeVisual.Points.Count > 0);
     }
 
-    /// <summary>IsBusy 時停用會改動幾何/場景的指令（匯入、旋轉、干涉），避免背景運算期間狀態被改走造成結果錯位</summary>
+    /// <summary>Disables scene-changing commands while background work runs.</summary>
     private bool IsIdle() => !IsBusy;
 
-    // ─── 匯入 ────────────────────────────────────────────────────
+    // Import
 
     [RelayCommand(CanExecute = nameof(IsIdle))]
     private async Task ImportAsync()
     {
         var dlg = new OpenFileDialog
         {
-            Title = "匯入 CAD 檔案（可複選）",
-            Filter = "CAD 檔案 (*.stp;*.step;*.stl;*.dxf)|*.stp;*.step;*.stl;*.dxf|" +
-                     "STEP (*.stp;*.step)|*.stp;*.step|STL (*.stl)|*.stl|DXF (*.dxf)|*.dxf|所有檔案 (*.*)|*.*",
+            Title = Get("Runtime.ImportTitle"),
+            Filter = Get("Runtime.ImportFilter"),
             Multiselect = true,
         };
         if (dlg.ShowDialog() == true)
             await ImportFilesAsync(dlg.FileNames);
     }
 
-    /// <summary>MRU 下拉點選（檔案可能已被移走 → ImportFilesAsync 會報匯入失敗）</summary>
+    /// <summary>Imports a recently opened file.</summary>
     [RelayCommand(CanExecute = nameof(IsIdle))]
     private Task ImportRecentAsync(string path) => ImportFilesAsync(new[] { path });
 
     public async Task ImportFilesAsync(IEnumerable<string> paths)
     {
         if (_viewport is null) return;
-        // 拖放/命令列可繞過指令 CanExecute 直接進來 → 匯入或背景運算期間直接擋掉，
-        // 避免兩批匯入交錯（StepImportService 有共享狀態，非重入安全）
-        if (IsBusy) { StatusText = "忙碌中（匯入或運算進行中），請稍候再匯入"; return; }
+        // Reject overlapping imports because StepImportService has shared state.
+        if (IsBusy) { SetStatus(() => Get("Runtime.ImportBusy")); return; }
         int ok = 0, fail = 0;
-        IsBusy = true; // 整批匯入期間維持 busy（v0.4.0：不再逐檔開關，杜絕檔案之間的重入空窗）
+        IsBusy = true;
         try
         {
             foreach (string path in paths)
             {
                 string name = Path.GetFileNameWithoutExtension(path);
-                StatusText = $"匯入中：{name} …";
-                // 匯入階段回報（從背景執行緒來 → 切回 UI 執行緒）
-                _importService.Progress = msg =>
+                SetStatus(() => Format("Runtime.Importing", name));
+                // Marshal progress from the import thread to the UI thread.
+                _importService.ProgressTextFor = textFor =>
                     System.Windows.Application.Current?.Dispatcher.BeginInvoke(
-                        () => StatusText = $"匯入 {name}：{msg}");
+                        () => SetStatus(() => Format("Runtime.ImportProgress", name, textFor())));
                 try
                 {
                     ImportedFileData data = await Task.Run(() => _importService.Import(path));
@@ -217,8 +228,9 @@ public partial class MainViewModel : ObservableObject
                 catch (Exception ex)
                 {
                     fail++;
-                    StatusText = $"匯入失敗：{name} — {ex.Message}";
-                    MessageBox.Show($"{path}\n\n{ex.Message}", "匯入失敗",
+                    string error = ex.Message;
+                    SetStatus(() => Format("Runtime.ImportFailed", name, error));
+                    MessageBox.Show($"{path}\n\n{error}", Get("Runtime.ImportFailedTitle"),
                         MessageBoxButton.OK, MessageBoxImage.Warning);
                 }
             }
@@ -231,7 +243,8 @@ public partial class MainViewModel : ObservableObject
         {
             if (SectionEnabled) ApplySection();
             _viewport.ZoomExtents(500);
-            StatusText = $"匯入完成：成功 {ok} 檔" + (fail > 0 ? $"、失敗 {fail} 檔" : "");
+            int succeeded = ok, failed = fail;
+            SetStatus(() => Format("Runtime.ImportCompleted", succeeded, failed > 0 ? Format("Runtime.ImportFailedCount", failed) : ""));
         }
     }
 
@@ -244,13 +257,13 @@ public partial class MainViewModel : ObservableObject
 
         ModelNodeViewModel root = BuildNode(data.Root, isRoot: true, data.FilePath, name);
 
-        // 邊線總量過大 → 整檔預設關閉（cascade；使用者可再開）
+        // Disable edges by default for very large files.
         int totalSegments = root.Leaves().Sum(l => (l.OriginalEdgePoints?.Count ?? 0) / 2);
         if (totalSegments > 30_000)
             root.ShowEdges = false;
 
         Roots.Add(root);
-        if (!string.IsNullOrWhiteSpace(TreeFilter)) root.ApplyFilter(TreeFilter); // 新檔套用目前過濾
+        if (!string.IsNullOrWhiteSpace(TreeFilter)) root.ApplyFilter(TreeFilter);
         foreach (ModelNodeViewModel leaf in root.Leaves())
         {
             leaf.VisualStateChanged += _ => SyncLeafVisuals(root);
@@ -258,7 +271,7 @@ public partial class MainViewModel : ObservableObject
                 _viewport!.Children.Add(leaf.BodyVisual);
         }
 
-        // 整檔合併成「一條」LinesVisual3D（轉動時只重建 1 條，避免逐零件 N 條造成卡頓）
+        // One merged edge visual per file avoids per-leaf rebuilds.
         if (root.Leaves().Any(l => l.OriginalEdgePoints is { Count: > 0 }))
         {
             root.EdgeVisual = new LinesVisual3D
@@ -275,6 +288,8 @@ public partial class MainViewModel : ObservableObject
         var vm = new ModelNodeViewModel(n.Faces.Count > 0 || n.EdgeSegments is not null ? _paletteIndex++ : _paletteIndex)
         {
             Name = overrideName ?? n.Name,
+            NameKey = overrideName is null ? n.NameKey : null,
+            NameNumber = n.NameNumber,
             FilePath = isRoot ? filePath : null,
             SolidCount = n.SolidCount,
             FaceCount = n.FaceCount,
@@ -285,7 +300,7 @@ public partial class MainViewModel : ObservableObject
 
         if (n.Faces.Count > 0)
         {
-            // leaf 共用材質（換色時只改 Brush）
+            // Share material across leaf faces for color changes.
             var diffuseBrush = new SolidColorBrush(vm.Color);
             diffuseBrush.Freeze();
             var diffuse = new DiffuseMaterial(diffuseBrush);
@@ -296,8 +311,7 @@ public partial class MainViewModel : ObservableObject
             backMat.Freeze();
             vm.SharedMaterial = diffuse;
 
-            // 一個 B-rep Face = 一個 GeometryModel3D，登錄反查表（剖面模式逐面拾取用）。
-            // 同時依面序記錄每面頂點起始邊界 + 對應 FaceInfo，供「命中合併網格反查面」（量測模式拾取用）。
+            // Keep one model per face for section picking and record merged-mesh face boundaries.
             var group = new Model3DGroup();
             var faceInfos = new FaceInfo[n.Faces.Count];
             var vertStarts = new int[n.Faces.Count + 1];
@@ -316,11 +330,9 @@ public partial class MainViewModel : ObservableObject
             vertStarts[n.Faces.Count] = vacc;
             vm.FacesContent = group;
 
-            // 合併網格：整零件所有面併成 1 個 GeometryModel3D（draw call 從每面 1 個降為每檔 1 個）。
-            // BuildMergedMesh 依 n.Faces 同序串接（baseIdx += positions.Count），與上面 vertStarts 對齊 → 命中頂點 index 可反查回面。
+            // BuildMergedMesh concatenates faces in the same order as vertStarts.
             var mergedModel = new GeometryModel3D(BuildMergedMesh(n.Faces), matGroup);
-            // 封閉實體背面不可見 → 不設 BackMaterial（WPF 兩面渲染成本砍半）；開放殼/STL 仍需背面。
-            // 拾取不受材質影響（WPF 3D hit-test 純幾何、不剔背面），故孔內壁仍可命中。
+            // Closed solids render front faces only; open shells and STL render both sides.
             if (n.SolidCount == 0 || !n.HasBrep)
                 mergedModel.BackMaterial = backMat;
             vm.MergedContent = new Model3DGroup();
@@ -328,14 +340,14 @@ public partial class MainViewModel : ObservableObject
             _mergedMap[mergedModel] = vm;
             _mergedFaceRanges[mergedModel] = (vertStarts, faceInfos);
 
-            // 非剖面一律顯示合併網格（瀏覽/量測都是，量測靠 _mergedFaceRanges 反查面）；只有剖面才逐面（裁切後幾何）
+            // Use merged meshes except in section mode, which needs separate clipped faces.
             vm.BodyVisual = new ModelVisual3D
             {
                 Content = SectionEnabled ? group : vm.MergedContent,
             };
         }
 
-        // 邊線端點僅保存於 leaf（資料）；實際 LinesVisual3D 由 root 合併建立（見 BuildRoot）
+        // Leaves hold edge data; roots hold the merged edge visual.
         if (n.EdgeSegments is { Count: > 0 })
             vm.OriginalEdgePoints = n.EdgeSegments;
 
@@ -354,8 +366,7 @@ public partial class MainViewModel : ObservableObject
     }
 
     /// <summary>
-    /// 重建整檔的合併邊線：收集所有「可見且開邊線」的 leaf 端點為單一 Point3DCollection。
-    /// 剖面開啟時即時裁切。一檔只有一條 LinesVisual3D → 轉動視角不再逐零件重建。
+    /// Rebuilds one edge visual from visible leaves, clipping segments in section mode.
     /// </summary>
     private void RefreshRootEdges(ModelNodeViewModel root)
     {
@@ -382,9 +393,9 @@ public partial class MainViewModel : ObservableObject
         else if (!shouldShow && contains) _viewport.Children.Remove(visual);
     }
 
-    // ─── 合併網格（瀏覽模式降 draw call）────────────────────────
+    // Merged meshes
 
-    /// <summary>把多個面網格依序併成單一 MeshGeometry3D（索引位移後串接；順序 = 呼叫端給的面序）</summary>
+    /// <summary>Concatenates face meshes in the given order.</summary>
     private static MeshGeometry3D MergeMeshes(IReadOnlyList<MeshGeometry3D> meshes)
     {
         int nv = 0, nt = 0;
@@ -411,7 +422,7 @@ public partial class MainViewModel : ObservableObject
         return mesh;
     }
 
-    /// <summary>匯入時建合併網格（依 faces 面序串接，與 _mergedFaceRanges 的頂點邊界對齊）</summary>
+    /// <summary>Builds the import mesh in face order for merged hit resolution.</summary>
     private static MeshGeometry3D BuildMergedMesh(IReadOnlyList<ImportedFace> faces)
     {
         var meshes = new List<MeshGeometry3D>(faces.Count);
@@ -419,8 +430,7 @@ public partial class MainViewModel : ObservableObject
         return MergeMeshes(meshes);
     }
 
-    /// <summary>重建合併網格（位置變更後，如零件平移）。由 leaf 逐面 fi.Mesh（未剖切原始）依 FacesContent 子序串接，
-    /// 與匯入時 BuildMergedMesh 的面序一致 → _mergedFaceRanges 頂點邊界維持有效。</summary>
+    /// <summary>Rebuilds a merged mesh after a transform without changing face vertex boundaries.</summary>
     private void RebuildMerged(ModelNodeViewModel leaf)
     {
         if (leaf.MergedContent is null || leaf.FacesContent is null) return;
@@ -432,13 +442,11 @@ public partial class MainViewModel : ObservableObject
     }
 
     /// <summary>
-    /// 依目前狀態切換每個 leaf 的渲染內容：
-    /// 非剖面（瀏覽 + 量測皆是）→ 合併網格（每檔 1 個 model，快）；量測拾取靠命中合併網格反查面（_mergedFaceRanges）。
-    /// 剖面 → 逐面（要顯示各面裁切後的幾何）。
+    /// Uses merged meshes for browsing and measurement; section mode uses separate clipped faces.
     /// </summary>
     private void ApplyRenderMode()
     {
-        // 量測不再需要逐面渲染（拾取打合併網格反查面）→ 只有剖面才逐面。永不在量測模式掛數萬個 GeometryModel3D。
+        // Measurement resolves merged-mesh hits back to their source faces.
         bool merged = !SectionEnabled;
         foreach (ModelNodeViewModel leaf in Roots.SelectMany(r => r.Leaves()))
         {
@@ -449,7 +457,7 @@ public partial class MainViewModel : ObservableObject
         }
     }
 
-    // ─── 節點操作 ────────────────────────────────────────────────
+    // Node commands
 
     [RelayCommand]
     private void ZoomNode(ModelNodeViewModel node)
@@ -461,14 +469,14 @@ public partial class MainViewModel : ObservableObject
     [RelayCommand]
     private void ZoomAll() => _viewport?.ZoomExtents(400);
 
-    /// <summary>標準視圖（機構慣例 Z 向上）：Iso / Front / Back / Top / Bottom / Left / Right</summary>
+    /// <summary>Standard views with Z up.</summary>
     [RelayCommand]
     private void SetStandardView(string name)
     {
         if (_viewport?.Camera is not ProjectionCamera cam) return;
         (Vector3D dir, Vector3D up) = name switch
         {
-            "Front"  => (new Vector3D(0, 1, 0),  new Vector3D(0, 0, 1)),  // 從 -Y 往 +Y 看
+            "Front"  => (new Vector3D(0, 1, 0),  new Vector3D(0, 0, 1)),
             "Back"   => (new Vector3D(0, -1, 0), new Vector3D(0, 0, 1)),
             "Top"    => (new Vector3D(0, 0, -1), new Vector3D(0, 1, 0)),
             "Bottom" => (new Vector3D(0, 0, 1),  new Vector3D(0, -1, 0)),
@@ -482,13 +490,13 @@ public partial class MainViewModel : ObservableObject
             : new Point3D(b.X + b.SizeX / 2, b.Y + b.SizeY / 2, b.Z + b.SizeZ / 2);
         double dist = Math.Max(SceneDiagonal() * 1.8, 10);
         cam.Position = center - dir * dist;
-        cam.LookDirection = dir * dist; // 目標點 = Position + LookDirection = 場景中心
+        cam.LookDirection = dir * dist;
         cam.UpDirection = up;
         _viewport.ZoomExtents(400);
-        StatusText = $"視圖：{name}";
+        SetStatus(() => Format("Runtime.View", Get($"Runtime.View{name}")));
     }
 
-    /// <summary>正交投影切換（平行投影，量尺寸不受透視變形；Helix 保持視角換相機型別）</summary>
+    /// <summary>Toggles orthographic projection while preserving the view angle.</summary>
     [ObservableProperty]
     private bool orthographicView;
 
@@ -496,7 +504,7 @@ public partial class MainViewModel : ObservableObject
     {
         if (_viewport is null) return;
         _viewport.Orthographic = value;
-        StatusText = value ? "正交投影（平行投影，適合尺寸確認）" : "透視投影";
+        SetStatus(() => Get(value ? "Runtime.Orthographic" : "Runtime.Perspective"));
     }
 
     [RelayCommand]
@@ -504,16 +512,16 @@ public partial class MainViewModel : ObservableObject
     {
         if (_viewport is null || !root.IsRoot) return;
 
-        if (ReferenceEquals(root, _gizmoTarget)) GizmoEnabled = false; // 目標被移除 → 收掉操作器
+        if (ReferenceEquals(root, _gizmoTarget)) GizmoEnabled = false;
 
-        // 量測 overlay 可能標在此檔模型上 → 一併清除（簡化：全清）
+        // Clear measurements that may be attached to the removed file.
         if (Measurements.Count > 0) ClearMeasurements();
 
         foreach (ModelNodeViewModel leaf in root.Leaves())
         {
             if (leaf.BodyVisual is not null)
                 _viewport.Children.Remove(leaf.BodyVisual);
-            if (leaf.FacesContent is not null) // 逐面群組才在 _faceMap（與目前顯示哪種內容無關）
+            if (leaf.FacesContent is not null)
                 foreach (Model3D m in leaf.FacesContent.Children)
                     _faceMap.Remove(m);
             if (leaf.MergedContent is not null)
@@ -526,18 +534,19 @@ public partial class MainViewModel : ObservableObject
         if (root.EdgeVisual is not null)
             _viewport.Children.Remove(root.EdgeVisual);
         Roots.Remove(root);
-        StatusText = $"已移除：{root.Name}";
+        string removedName = root.Name;
+        SetStatus(() => Format("Runtime.Removed", removedName));
     }
 
-    // ─── 顯示控制 / 體積（樹右鍵選單）────────────────────────────
+    // Visibility and volume
 
-    /// <summary>只顯示此節點（其餘全部隱藏；「全部顯示」復原）</summary>
+    /// <summary>Shows only this node until ShowAll is called.</summary>
     [RelayCommand]
     private void IsolateNode(ModelNodeViewModel node)
     {
         foreach (ModelNodeViewModel r in Roots) SetVisibleRecursive(r, false);
         SetVisibleRecursive(node, true);
-        StatusText = $"只顯示「{node.Name}」（樹右鍵 → 全部顯示 復原）";
+        SetStatus(() => Format("Runtime.Isolated", node.Name));
     }
 
     [RelayCommand]
@@ -545,25 +554,24 @@ public partial class MainViewModel : ObservableObject
     {
         foreach (ModelNodeViewModel l in Roots.SelectMany(r => r.Leaves()))
             l.IsVisible = !l.IsVisible;
-        StatusText = "已反轉顯示";
+        SetStatus(() => Get("Runtime.VisibilityInverted"));
     }
 
     [RelayCommand]
     private void ShowAll()
     {
         foreach (ModelNodeViewModel r in Roots) SetVisibleRecursive(r, true);
-        StatusText = "已全部顯示";
+        SetStatus(() => Get("Runtime.AllVisible"));
     }
 
-    /// <summary>逐節點顯式遞迴設定可見性。不能只設 root（setter 同值不觸發 cascade，
-    /// 之前的隔離操作可能留下「父關子開」的混合狀態）</summary>
+    /// <summary>Sets visibility for every node, including mixed child states.</summary>
     private static void SetVisibleRecursive(ModelNodeViewModel node, bool visible)
     {
         node.IsVisible = visible;
         foreach (ModelNodeViewModel c in node.Children) SetVisibleRecursive(c, visible);
     }
 
-    /// <summary>體積/質心（網格 signed volume，封閉實體才可靠）→ 加進量測結果 + 質心標記</summary>
+    /// <summary>Adds a volume and centroid measurement for a closed mesh.</summary>
     [RelayCommand]
     private void MeasureVolume(ModelNodeViewModel node)
     {
@@ -576,14 +584,14 @@ public partial class MainViewModel : ObservableObject
             .ToList();
         if (meshes.Count == 0)
         {
-            StatusText = $"「{node.Name}」沒有可計算的面網格（線架構無體積）";
+            SetStatus(() => Format("Runtime.VolumeNoMesh", node.Name));
             return;
         }
 
         (double vol, Point3D centroid, bool reliable) = MeasurementService.MeshVolume(meshes);
         if (!reliable)
         {
-            StatusText = $"「{node.Name}」非封閉網格（開放殼），無法可靠計算體積";
+            SetStatus(() => Format("Runtime.VolumeOpenMesh", node.Name));
             return;
         }
 
@@ -596,9 +604,7 @@ public partial class MainViewModel : ObservableObject
         {
             Kind = MeasureMode.Volume,
             TitleFor = u => $"{label}  {name}  V ≈ {Units.V(vol, u)}",
-            DetailFor = u => $"體積 ≈ {Units.V(vol, u)}（網格近似）\n質心 {Units.P(centroid, u)}\n" +
-                             $"外形（AABB）{Units.C(b.SizeX, u)} × {Units.C(b.SizeY, u)} × {Units.C(b.SizeZ, u)} " +
-                             (u == UnitSystem.Millimeter ? "mm" : "in"),
+            DetailFor = u => Format("Runtime.VolumeDetail", Units.V(vol, u), Units.P(centroid, u), Units.C(b.SizeX, u), Units.C(b.SizeY, u), Units.C(b.SizeZ, u), u == UnitSystem.Millimeter ? "mm" : "in"),
         };
         m.Overlays.Add(new SphereVisual3D { Center = centroid, Radius = markerR, Fill = Brushes.OrangeRed });
         var volLabel = new BillboardTextVisual3D
@@ -615,46 +621,47 @@ public partial class MainViewModel : ObservableObject
         AddMeasurement(m);
     }
 
-    // ─── 量測 ────────────────────────────────────────────────────
+    // Measurement
 
     partial void OnCurrentModeChanged(MeasureMode value)
     {
         CancelPending();
-        ApplyRenderMode(); // 非剖面一律合併網格（量測拾取靠反查面）；不再因切量測模式而掛逐面
-        StatusText = value switch
+        ApplyRenderMode();
+        string? key = value switch
         {
-            MeasureMode.None => "瀏覽模式（右鍵旋轉、滾輪縮放、中鍵或 Shift+左鍵拖曳平移）",
-            MeasureMode.Point => "點量測：點擊模型表面（自動吸附鄰近頂點）",
-            MeasureMode.Distance => "距離量測：點選第 1 點",
-            MeasureMode.Edge => "邊量測：點擊靠近要量的邊",
-            MeasureMode.Face => "面量測：點擊要量的面",
-            MeasureMode.Circle => "圓量測：點擊圓孔內壁或圓邊附近",
-            MeasureMode.Angle => "角度量測：點選第 1 個面（或靠近直線邊）",
-            MeasureMode.FaceDistance => "面距量測：點選第 1 個面",
-            MeasureMode.Align => "兩點對齊：先點「要移動零件」上的點，再點目標點（純平移，量測會清空）",
-            MeasureMode.Align3 => "三點對齊：先在「要移動的檔案」點 3 個特徵點，再到目標檔案點 3 個對應點（旋轉+平移）",
-            MeasureMode.Drag => "拖曳模式：左鍵按住零件拖動（沿螢幕平面），放開定位；深度方向先轉視角再拖。右鍵仍可轉視角",
-            _ => StatusText,
+            MeasureMode.None => "Runtime.ModeBrowse",
+            MeasureMode.Point => "Runtime.ModePoint",
+            MeasureMode.Distance => "Runtime.ModeDistance",
+            MeasureMode.Edge => "Runtime.ModeEdge",
+            MeasureMode.Face => "Runtime.ModeFace",
+            MeasureMode.Circle => "Runtime.ModeCircle",
+            MeasureMode.Angle => "Runtime.ModeAngle",
+            MeasureMode.FaceDistance => "Runtime.ModeFaceDistance",
+            MeasureMode.Align => "Runtime.ModeAlign",
+            MeasureMode.Align3 => "Runtime.ModeAlign3",
+            MeasureMode.Drag => "Runtime.ModeDrag",
+            _ => null,
         };
+        if (key is not null) SetStatus(() => Get(key));
     }
 
     partial void OnUseInchChanged(bool value)
     {
         UnitSystem u = CurrentUnit;
         foreach (MeasurementResult m in Measurements) m.SetUnit(u);
-        StatusText = value ? "顯示單位：inch" : "顯示單位：mm";
+        SetStatus(() => Get(value ? "Runtime.UnitInch" : "Runtime.UnitMillimeter"));
     }
 
-    /// <summary>Esc（MainWindow 轉發）：先取消進行中的多段量測（保留模式），再按退回瀏覽模式；再退操作器</summary>
+    /// <summary>Cancels a pending pick, then exits measurement mode or closes the gizmo.</summary>
     public void OnEscape()
     {
-        if (CancelSectionPickIfActive()) return; // 3點剖面定義中 → 先取消定義
+        if (CancelSectionPickIfActive()) return;
         bool hadPending = _pendingPoint is not null || _pendingDirection is not null ||
                           _pendingFace is not null || _pendingAlign is not null || _align3.Count > 0;
         if (hadPending)
         {
             CancelPending();
-            StatusText = "已取消目前量測起點（再按 Esc 退出量測模式）";
+            SetStatus(() => Get("Runtime.MeasurementStartCancelled"));
         }
         else if (CurrentMode != MeasureMode.None)
         {
@@ -666,7 +673,7 @@ public partial class MainViewModel : ObservableObject
         }
     }
 
-    /// <summary>量測模式快速鍵（MainWindow 轉發；無修飾鍵）。同鍵再按 = 退回瀏覽。回傳 false 表示非快速鍵。</summary>
+    /// <summary>Handles measurement hotkeys; repeating a key returns to browse mode.</summary>
     public bool OnHotKey(System.Windows.Input.Key key)
     {
         MeasureMode? m = key switch
@@ -685,11 +692,11 @@ public partial class MainViewModel : ObservableObject
         return true;
     }
 
-    /// <summary>MainWindow 滑鼠左鍵點擊轉發進來</summary>
+    /// <summary>Handles left-clicks forwarded by MainWindow.</summary>
     public void OnViewportClick(Point position)
     {
         if (_viewport is null || IsBusy) return;
-        if (HandleSectionPlanePick(position)) return; // 3點剖面定義模式優先吃點擊（v0.5.0）
+        if (HandleSectionPlanePick(position)) return;
         if (CurrentMode is MeasureMode.None or MeasureMode.Drag) return;
 
         var hits = _viewport.Viewport.FindHits(position);
@@ -699,13 +706,13 @@ public partial class MainViewModel : ObservableObject
         foreach (var h in hits)
         {
             if (h.Model is null) continue;
-            // 剖面模式：渲染逐面 → 直接查 _faceMap
+            // Section mode renders individual faces.
             if (_faceMap.TryGetValue(h.Model, out FaceInfo? f))
             {
                 fi = f; hitPoint = h.Position; hitNormal = h.Normal;
                 break;
             }
-            // 量測/瀏覽模式：渲染合併網格 → 用命中三角形頂點 index 反查回是哪個面
+            // Other modes resolve merged-mesh vertex indices to faces.
             if (h.RayHit is not null && _mergedFaceRanges.TryGetValue(h.Model, out var range))
             {
                 FaceInfo? mf = ResolveMergedFace(range, h.RayHit.VertexIndex1);
@@ -718,7 +725,7 @@ public partial class MainViewModel : ObservableObject
         }
         if (fi is null)
         {
-            StatusText = "未命中模型表面";
+            SetStatus(() => Get("Runtime.NoSurfaceHit"));
             return;
         }
 
@@ -728,17 +735,18 @@ public partial class MainViewModel : ObservableObject
         }
         catch (Exception ex)
         {
-            StatusText = $"量測失敗：{ex.Message}";
+            string error = ex.Message;
+            SetStatus(() => Format("Runtime.MeasureFailed", error));
         }
     }
 
-    /// <summary>命中合併網格的某頂點 index → 反查回是哪個面（依面序的頂點起始邊界二分搜尋）。</summary>
+    /// <summary>Finds the source face for a merged-mesh vertex by binary search.</summary>
     private static FaceInfo? ResolveMergedFace((int[] Starts, FaceInfo[] Faces) range, int vertexIndex)
     {
         int[] starts = range.Starts;
         FaceInfo[] faces = range.Faces;
         if (vertexIndex < 0 || faces.Length == 0 || vertexIndex >= starts[faces.Length]) return null;
-        // 找最大的 k 使 starts[k] <= vertexIndex（face k 佔頂點 [starts[k], starts[k+1])）
+        // Find the largest face start not exceeding the hit vertex index.
         int lo = 0, hi = faces.Length - 1, ans = 0;
         while (lo <= hi)
         {
@@ -755,10 +763,10 @@ public partial class MainViewModel : ObservableObject
         double snapTol = diag * 0.02;
         double markerR = Math.Clamp(diag * 0.004, 0.01, 5.0);
 
-        // 無 B-rep 來源（STL）只支援部分模式
+        // STL has no B-rep edges or faces for these modes.
         if (fi.BrepFace is null && CurrentMode is MeasureMode.Edge or MeasureMode.Circle or MeasureMode.Face)
         {
-            StatusText = "此模型無 B-rep（STL/網格），僅支援 點 / 距離 / 角度 / 面距 量測";
+            SetStatus(() => Get("Runtime.MeshMeasurementLimited"));
             return;
         }
 
@@ -777,7 +785,7 @@ public partial class MainViewModel : ObservableObject
                 {
                     _pendingPoint = p;
                     AddPendingMarker(p, markerR);
-                    StatusText = $"第 1 點 ({p.X:F2}, {p.Y:F2}, {p.Z:F2}) — 點選第 2 點";
+                    SetStatus(() => Format("Runtime.DistanceFirstPoint", p.X, p.Y, p.Z));
                 }
                 else
                 {
@@ -791,7 +799,7 @@ public partial class MainViewModel : ObservableObject
             case MeasureMode.Edge:
             {
                 var result = _measureService.MeasureEdge(fi, hit, NextLabel(MeasureMode.Edge, "E"), markerR, circlesOnly: false);
-                if (result is null) { StatusText = "此面沒有可量測的邊"; UndoLabel(MeasureMode.Edge); }
+                if (result is null) { SetStatus(() => Get("Runtime.NoMeasurableEdge")); UndoLabel(MeasureMode.Edge); }
                 else AddMeasurement(result);
                 break;
             }
@@ -803,7 +811,7 @@ public partial class MainViewModel : ObservableObject
             case MeasureMode.Circle:
             {
                 var result = _measureService.MeasureEdge(fi, hit, NextLabel(MeasureMode.Circle, "C"), markerR, circlesOnly: true);
-                if (result is null) { StatusText = "此面沒有圓形邊（請點圓孔內壁或圓邊附近）"; UndoLabel(MeasureMode.Circle); }
+                if (result is null) { SetStatus(() => Get("Runtime.NoCircularEdge")); UndoLabel(MeasureMode.Circle); }
                 else AddMeasurement(result);
                 break;
             }
@@ -814,7 +822,7 @@ public partial class MainViewModel : ObservableObject
                 {
                     _pendingDirection = pick;
                     AddPendingMarker(pick.At, markerR);
-                    StatusText = $"已選第 1 個方向（{pick.Desc}）— 點選第 2 個面或邊";
+                    SetStatus(() => Format("Runtime.AngleFirstDirection", Get(pick.Desc)));
                 }
                 else
                 {
@@ -831,11 +839,11 @@ public partial class MainViewModel : ObservableObject
                 {
                     _pendingFace = fi;
                     AddPendingMarker(hit, markerR);
-                    StatusText = "已選第 1 個面 — 點選另一個面";
+                    SetStatus(() => Get("Runtime.FaceDistanceFirstFace"));
                 }
                 else if (ReferenceEquals(_pendingFace, fi))
                 {
-                    StatusText = "兩次點到同一個面，請點選另一個面";
+                    SetStatus(() => Get("Runtime.SameFace"));
                 }
                 else
                 {
@@ -850,16 +858,16 @@ public partial class MainViewModel : ObservableObject
             {
                 Point3D p = _measureService.Snap(fi, hit, snapTol);
                 ModelNodeViewModel? root = FindRootOf(fi.Owner);
-                if (root is null) { StatusText = "找不到此零件所屬檔案"; break; }
+                if (root is null) { SetStatus(() => Get("Runtime.RootNotFound")); break; }
                 if (_pendingAlign is null)
                 {
                     _pendingAlign = (root, p);
                     AddPendingMarker(p, markerR);
-                    StatusText = $"將移動「{root.Name}」— 點選目標點（另一個檔案上）";
+                    SetStatus(() => Format("Runtime.AlignMoving", root.Name));
                 }
                 else if (ReferenceEquals(_pendingAlign.Value.Root, root))
                 {
-                    StatusText = "目標點要點在另一個檔案上（兩點同屬一個檔案無法對齊）";
+                    SetStatus(() => Get("Runtime.AlignOtherFile"));
                 }
                 else
                 {
@@ -867,8 +875,7 @@ public partial class MainViewModel : ObservableObject
                     Vector3D offset = p - from;
                     CancelPending();
                     TranslateRoot(moveRoot, offset);
-                    StatusText = $"已移動「{moveRoot.Name}」 Δ({offset.X:F3}, {offset.Y:F3}, {offset.Z:F3}) mm" +
-                                 "（量測已清空；可用 ⇔面距 / 🧩干涉 驗證配合）";
+                    SetStatus(() => Format("Runtime.AlignMoved", moveRoot.Name, offset.X, offset.Y, offset.Z));
                 }
                 break;
             }
@@ -876,43 +883,46 @@ public partial class MainViewModel : ObservableObject
             {
                 Point3D p = _measureService.Snap(fi, hit, snapTol);
                 ModelNodeViewModel? root = FindRootOf(fi.Owner);
-                if (root is null) { StatusText = "找不到此零件所屬檔案"; break; }
+                if (root is null) { SetStatus(() => Get("Runtime.RootNotFound")); break; }
 
-                if (_align3.Count < 3) // 來源 3 點（要移動的檔案）
+                if (_align3.Count < 3)
                 {
                     if (_align3.Count > 0 && !ReferenceEquals(_align3[0].Root, root))
                     {
-                        StatusText = $"來源 3 點要同一個檔案（要移動：{_align3[0].Root.Name}）";
+                        ModelNodeViewModel sourceRoot = _align3[0].Root;
+                        SetStatus(() => Format("Runtime.Align3SameSource", sourceRoot.Name));
                         break;
                     }
                     if (_align3.Count == 2 && RigidAlign.Collinear(_align3[0].P, _align3[1].P, p))
                     {
-                        StatusText = "三點共線，請改選不共線的第 3 點";
+                        SetStatus(() => Get("Runtime.Align3SourceCollinear"));
                         break;
                     }
                     _align3.Add((root, p));
                     AddPendingMarker(p, markerR);
-                    StatusText = _align3.Count < 3
-                        ? $"來源點 {_align3.Count}/3 — 繼續點「{root.Name}」上的點"
-                        : "來源 3 點完成 — 換點「目標檔案」上的對應點 1/3";
+                    int sourceCount = _align3.Count;
+                    SetStatus(() => sourceCount < 3
+                        ? Format("Runtime.Align3SourcePoint", sourceCount, root.Name)
+                        : Get("Runtime.Align3SourceComplete"));
                 }
-                else // 目標 3 點（另一個檔案，順序對應來源點）
+                else
                 {
                     if (ReferenceEquals(_align3[0].Root, root))
                     {
-                        StatusText = "目標點要點在另一個檔案上";
+                        SetStatus(() => Get("Runtime.Align3OtherFile"));
                         break;
                     }
                     if (_align3.Count == 5 && RigidAlign.Collinear(_align3[3].P, _align3[4].P, p))
                     {
-                        StatusText = "目標三點共線，請改選不共線的第 3 點";
+                        SetStatus(() => Get("Runtime.Align3TargetCollinear"));
                         break;
                     }
                     _align3.Add((root, p));
                     AddPendingMarker(p, markerR);
                     if (_align3.Count < 6)
                     {
-                        StatusText = $"目標點 {_align3.Count - 3}/3 — 繼續點目標檔案上的對應點";
+                        int targetCount = _align3.Count - 3;
+                        SetStatus(() => Format("Runtime.Align3TargetPoint", targetCount));
                         break;
                     }
 
@@ -922,11 +932,11 @@ public partial class MainViewModel : ObservableObject
                     CancelPending();
                     if (!RigidAlign.TryRigidTransform(p1, p2, p3, q1, q2, q3, out Matrix3D m))
                     {
-                        StatusText = "三點對齊失敗（點位退化），請重新選點";
+                        SetStatus(() => Get("Runtime.Align3Failed"));
                         break;
                     }
                     TransformRoot(moveRoot, RigidAlign.ToModOp(m), m);
-                    StatusText = $"已三點對齊「{moveRoot.Name}」（旋轉+平移；點1精確貼合，量測已清空，可用 🧩干涉 驗證）";
+                    SetStatus(() => Format("Runtime.Align3Completed", moveRoot.Name));
                 }
                 break;
             }
@@ -961,7 +971,8 @@ public partial class MainViewModel : ObservableObject
         Measurements.Add(result);
         foreach (Visual3D v in result.Overlays)
             _viewport!.Children.Add(v);
-        StatusText = $"✓ {result.Title}";
+        Func<UnitSystem, string> titleFor = result.TitleFor;
+        SetStatus(() => $"✓ {titleFor(CurrentUnit)}");
     }
 
     [RelayCommand]
@@ -981,7 +992,7 @@ public partial class MainViewModel : ObservableObject
         Measurements.Clear();
         _counters.Clear();
         CancelPending();
-        StatusText = "已清除全部量測";
+        SetStatus(() => Get("Runtime.MeasurementsCleared"));
     }
 
     private void CancelPending()
@@ -996,7 +1007,7 @@ public partial class MainViewModel : ObservableObject
         _align3.Clear();
     }
 
-    // ─── 零件剛體變換（兩點對齊=平移、旋轉 90°、三點對齊=旋轉+平移）──
+    // Rigid part transforms
 
     private void TranslateRoot(ModelNodeViewModel root, Vector3D v)
     {
@@ -1007,27 +1018,25 @@ public partial class MainViewModel : ObservableObject
     }
 
     /// <summary>
-    /// 對整個檔案（root）套剛體變換：B-rep 用 ModOp 整體 Modify（量測維持精確）、
-    /// 渲染網格 / 合併網格 / 邊線端點同步重算、邊界重新計算。
-    /// op 與 m 必須是同一個變換（CADability 與 WPF 兩種表示）。
+    /// Transforms B-rep objects, meshes, edges and bounds for one file.
+    /// op and m must represent the same transform in CADability and WPF conventions.
     /// </summary>
     private void TransformRoot(ModelNodeViewModel root, CADability.ModOp op, Matrix3D m)
     {
         if (_viewport is null) return;
-        ClearMeasurements(); // 量測標記位置已失效
+        ClearMeasurements();
 
         var leaves = root.Leaves().ToList();
 
-        // B-rep：對 Solid/Shell 整體 Modify（避免共用邊被逐面重複變換）。
-        // CADability 物件非執行緒安全 → 維持循序
+        // Transform whole B-rep objects sequentially to avoid shared-edge changes.
         foreach (ModelNodeViewModel leaf in leaves)
             foreach (CADability.GeoObject.IGeoObject g in leaf.SourceGeos)
             {
                 try { g.Modify(op); }
-                catch { /* 個別物件變換失敗不中斷 */ }
+                catch { }
             }
 
-        // 渲染網格：面級平行變換（來源/輸出皆 frozen、各面獨立 → 安全；大檔 64k 面吃滿多核）
+        // Transform independent frozen face meshes in parallel.
         var faceItems = new List<(GeometryModel3D Gm, FaceInfo Fi)>();
         foreach (ModelNodeViewModel leaf in leaves)
             if (leaf.FacesContent is not null)
@@ -1037,7 +1046,7 @@ public partial class MainViewModel : ObservableObject
 
         var moved = new MeshGeometry3D[faceItems.Count];
         Parallel.For(0, faceItems.Count, i => moved[i] = TransformMesh(faceItems[i].Fi.Mesh, m));
-        for (int i = 0; i < faceItems.Count; i++) // 視覺樹賦值回 UI 執行緒循序做
+        for (int i = 0; i < faceItems.Count; i++)
         {
             faceItems[i].Fi.Mesh = moved[i];
             faceItems[i].Gm.Geometry = moved[i];
@@ -1046,15 +1055,15 @@ public partial class MainViewModel : ObservableObject
         foreach (ModelNodeViewModel leaf in leaves)
         {
             if (leaf.FacesContent is not null)
-                RebuildMerged(leaf); // 合併網格同步
+                RebuildMerged(leaf);
 
-            // 邊線端點（資料）；實際合併線於迴圈後重建
+            // Update edge data before rebuilding the merged visual.
             if (leaf.OriginalEdgePoints is not null)
                 leaf.OriginalEdgePoints = TransformPoints(leaf.OriginalEdgePoints, m);
         }
 
         RecomputeBounds(root);
-        if (SectionEnabled) ApplySection(); // 內含 RefreshRootEdges
+        if (SectionEnabled) ApplySection();
         else RefreshRootEdges(root);
     }
 
@@ -1065,7 +1074,7 @@ public partial class MainViewModel : ObservableObject
         var mesh = new MeshGeometry3D
         {
             Positions = positions,
-            TriangleIndices = src.TriangleIndices, // frozen，可共用（法向量缺省由 WPF 自算）
+            TriangleIndices = src.TriangleIndices,
         };
         mesh.Freeze();
         return mesh;
@@ -1079,7 +1088,7 @@ public partial class MainViewModel : ObservableObject
         return pts;
     }
 
-    /// <summary>旋轉後 AABB 不能只平移 → 由網格/邊線重新計算（bottom-up）</summary>
+    /// <summary>Recomputes bounds from transformed meshes and edges.</summary>
     private Rect3D RecomputeBounds(ModelNodeViewModel node)
     {
         Rect3D b = Rect3D.Empty;
@@ -1101,7 +1110,7 @@ public partial class MainViewModel : ObservableObject
         return b;
     }
 
-    // ─── 旋轉 90°（樹面板選取的檔案，繞其中心）──────────────────
+    // Rotate selected file
 
     [RelayCommand(CanExecute = nameof(IsIdle))]
     private void RotateRoot(string axisName)
@@ -1110,7 +1119,7 @@ public partial class MainViewModel : ObservableObject
             : Roots.Count == 1 ? Roots[0] : null;
         if (root is null)
         {
-            StatusText = "請先在樹面板點選要旋轉的檔案（任一節點即可）";
+            SetStatus(() => Get("Runtime.RotateSelectFile"));
             return;
         }
         Rect3D b = root.Bounds;
@@ -1126,7 +1135,7 @@ public partial class MainViewModel : ObservableObject
         var m = Matrix3D.Identity;
         m.RotateAt(new Quaternion(axis, 90), center);
         TransformRoot(root, RigidAlign.ToModOp(m), m);
-        StatusText = $"已旋轉「{root.Name}」繞 {axisName} 軸 +90°（再按可繼續轉）";
+        SetStatus(() => Format("Runtime.Rotated", root.Name, axisName));
     }
 
     private ModelNodeViewModel? RootContaining(ModelNodeViewModel node) =>
@@ -1135,9 +1144,9 @@ public partial class MainViewModel : ObservableObject
     private static bool ContainsNode(ModelNodeViewModel parent, ModelNodeViewModel target) =>
         parent.Children.Any(c => ReferenceEquals(c, target) || ContainsNode(c, target));
 
-    // 三點對齊的剛體變換數學在 Services/RigidAlign.cs（SmokeTest --align-test 驗證）
+    // Three-point alignment math is in RigidAlign.
 
-    // ─── 共用 ────────────────────────────────────────────────────
+    // Shared helpers
 
     private Rect3D UnionBounds()
     {
diff --git a/src/STPViewer/ViewModels/ModelNodeViewModel.cs b/src/STPViewer/ViewModels/ModelNodeViewModel.cs
index 711e640..2489dd6 100644
--- a/src/STPViewer/ViewModels/ModelNodeViewModel.cs
+++ b/src/STPViewer/ViewModels/ModelNodeViewModel.cs
@@ -7,34 +7,35 @@ using System.Windows.Media.Media3D;
 using CommunityToolkit.Mvvm.ComponentModel;
 using CommunityToolkit.Mvvm.Input;
 using HelixToolkit.Wpf;
+using STPViewer.Services;
 
 namespace STPViewer.ViewModels;
 
 /// <summary>
-/// 裝配樹節點：root = 匯入檔、group = STEP 裝配（Block）、leaf = 零件幾何。
-/// 可見性 / 邊線 / 顏色設定向下層疊（cascade）。
+/// Assembly tree node: imported file, STEP group, or geometry leaf.
+/// Visibility, edges, and color cascade to children.
 /// </summary>
 public partial class ModelNodeViewModel : ObservableObject
 {
-    /// <summary>調色盤（每個 leaf 依序取色，點色塊循環切換）</summary>
+    /// <summary>Palette used when assigning and cycling leaf colors.</summary>
     public static readonly Color[] Palette =
     {
-        Color.FromRgb(0x90, 0xA4, 0xAE), // 藍灰（金屬感）
-        Color.FromRgb(0x4F, 0xC3, 0xF7), // 淺藍
-        Color.FromRgb(0xFF, 0xB7, 0x4D), // 橙
-        Color.FromRgb(0x81, 0xC7, 0x84), // 綠
-        Color.FromRgb(0xBA, 0x68, 0xC8), // 紫
-        Color.FromRgb(0xE5, 0x73, 0x73), // 紅
-        Color.FromRgb(0xFF, 0xD5, 0x4F), // 黃
-        Color.FromRgb(0x4D, 0xB6, 0xAC), // 藍綠
-        Color.FromRgb(0xA1, 0x88, 0x7F), // 棕
-        Color.FromRgb(0x79, 0x86, 0xCB), // 靛藍
+        Color.FromRgb(0x90, 0xA4, 0xAE),
+        Color.FromRgb(0x4F, 0xC3, 0xF7),
+        Color.FromRgb(0xFF, 0xB7, 0x4D),
+        Color.FromRgb(0x81, 0xC7, 0x84),
+        Color.FromRgb(0xBA, 0x68, 0xC8),
+        Color.FromRgb(0xE5, 0x73, 0x73),
+        Color.FromRgb(0xFF, 0xD5, 0x4F),
+        Color.FromRgb(0x4D, 0xB6, 0xAC),
+        Color.FromRgb(0xA1, 0x88, 0x7F),
+        Color.FromRgb(0x79, 0x86, 0xCB),
     };
 
     [ObservableProperty]
     private bool isVisible = true;
 
-    /// <summary>輪廓邊線開關（邊線量過大的檔案匯入時自動關閉，避免轉動視角卡頓）</summary>
+    /// <summary>Outline visibility.</summary>
     [ObservableProperty]
     private bool showEdges = true;
 
@@ -44,9 +45,17 @@ public partial class ModelNodeViewModel : ObservableObject
     [ObservableProperty]
     private Color color;
 
-    public string Name { get; init; } = "";
+    public string Name
+    {
+        get => NameKey is null ? _name : NameNumber > 0 && NameKey == "Runtime.MeshNameNumbered"
+            ? LocalizationService.Format(NameKey, NameNumber) : LocalizationService.Get(NameKey);
+        init => _name = value;
+    }
+    private string _name = "";
+    public string? NameKey { get; init; }
+    public int NameNumber { get; init; }
 
-    /// <summary>root（檔案層級）才有值</summary>
+    /// <summary>Set only on imported file roots.</summary>
     public string? FilePath { get; init; }
     public bool IsRoot => FilePath is not null;
 
@@ -57,7 +66,7 @@ public partial class ModelNodeViewModel : ObservableObject
     public int FaceCount { get; init; }
     public int TriangleCount { get; init; }
 
-    /// <summary>世界座標邊界（零件平移/旋轉後由 RecomputeBounds 更新；連動 Stats/Tooltip 的外形尺寸）</summary>
+    /// <summary>World-space bounds updated after part transforms.</summary>
     public Rect3D Bounds
     {
         get => _bounds;
@@ -71,31 +80,39 @@ public partial class ModelNodeViewModel : ObservableObject
     }
     private Rect3D _bounds = Rect3D.Empty;
 
-    /// <summary>外形尺寸 L×W×H（AABB，mm）</summary>
+    /// <summary>Axis-aligned size in millimeters.</summary>
     public string SizeText => Bounds.IsEmpty
         ? ""
         : $"{Bounds.SizeX:F1} × {Bounds.SizeY:F1} × {Bounds.SizeZ:F1} mm";
 
-    /// <summary>來源 B-rep 物件（零件平移時整體 Modify，避免共用邊被重複位移）</summary>
+    /// <summary>Source B-rep objects transformed as whole parts.</summary>
     public List<CADability.GeoObject.IGeoObject> SourceGeos { get; } = new();
 
-    /// <summary>false = STL/曲線等無 B-rep 來源（邊/面/圓量測不可用）</summary>
+    /// <summary>False for STL or curve-only sources without B-rep geometry.</summary>
     public bool HasBrep { get; init; } = true;
 
     public string Stats =>
-        $"{SolidCount} 實體 · {FaceCount} 面 · {TriangleCount:N0} △" + (HasBrep ? "" : " · 無B-rep") +
-        (Bounds.IsEmpty ? "" : $"\n外形 {SizeText}");
+        LocalizationService.Format("Runtime.NodeStats", SolidCount, FaceCount, TriangleCount) +
+        (HasBrep ? "" : LocalizationService.Get("Runtime.NoBrep")) +
+        (Bounds.IsEmpty ? "" : LocalizationService.Format("Runtime.OutlineSize", SizeText));
 
     public string ToolTipText => (FilePath is not null ? FilePath + "\n" : "") + Stats;
 
-    // ── 樹搜尋/過濾（只影響樹面板顯示，不影響 3D 可見性）──
+    public void RefreshLocalizedText()
+    {
+        OnPropertyChanged(nameof(Name));
+        OnPropertyChanged(nameof(Stats));
+        OnPropertyChanged(nameof(ToolTipText));
+        foreach (ModelNodeViewModel child in Children) child.RefreshLocalizedText();
+    }
+
+    // Tree filtering does not change viewport visibility.
 
     [ObservableProperty]
     private bool isFilterVisible = true;
 
     /// <summary>
-    /// 套用名稱過濾：符合者 + 其祖先 + 其子樹 顯示。空字串 = 全顯。
-    /// 過濾中有符合的子孫時自動展開。回傳此節點是否顯示。
+    /// Shows matching nodes, their ancestors and descendants; expands matching branches.
     /// </summary>
     public bool ApplyFilter(string? filter, bool ancestorMatched = false)
     {
@@ -109,17 +126,17 @@ public partial class ModelNodeViewModel : ObservableObject
         return IsFilterVisible;
     }
 
-    // ── 視覺物件 ──
-    public ModelVisual3D? BodyVisual { get; set; }          // leaf：面網格容器（內容在兩種模式間切換）
-    public Model3DGroup? FacesContent { get; set; }         // leaf：逐面 GeometryModel3D（量測拾取用）
-    public Model3DGroup? MergedContent { get; set; }        // leaf：整零件合併成 1 個 GeometryModel3D（瀏覽用，draw call 大減）
-    public LinesVisual3D? EdgeVisual { get; set; }          // root：整檔合併邊線（一檔一條，避免轉動卡頓）
+    // Viewport objects
+    public ModelVisual3D? BodyVisual { get; set; }
+    public Model3DGroup? FacesContent { get; set; }
+    public Model3DGroup? MergedContent { get; set; }
+    public LinesVisual3D? EdgeVisual { get; set; }
     public DiffuseMaterial? SharedMaterial { get; set; }
 
-    /// <summary>原始（未剖切）邊線端點 — 剖面還原用</summary>
+    /// <summary>Unclipped edge endpoints used for section restoration.</summary>
     public Point3DCollection? OriginalEdgePoints { get; set; }
 
-    /// <summary>leaf 的可見性/邊線狀態變更（MainViewModel 同步 viewport）</summary>
+    /// <summary>Signals the ViewModel to update leaf viewport objects.</summary>
     public event Action<ModelNodeViewModel>? VisualStateChanged;
 
     private int _paletteIndex;
@@ -130,7 +147,7 @@ public partial class ModelNodeViewModel : ObservableObject
         color = Palette[_paletteIndex];
     }
 
-    /// <summary>所有 leaf 後代（含自身若為 leaf）</summary>
+    /// <summary>All descendant leaves, including this node when it is a leaf.</summary>
     public IEnumerable<ModelNodeViewModel> Leaves()
     {
         if (IsLeafNode) { yield return this; yield break; }
diff --git a/src/STPViewer/ViewModels/QuickBarViewModel.cs b/src/STPViewer/ViewModels/QuickBarViewModel.cs
index d3075d2..f40888a 100644
--- a/src/STPViewer/ViewModels/QuickBarViewModel.cs
+++ b/src/STPViewer/ViewModels/QuickBarViewModel.cs
@@ -3,14 +3,16 @@ using System.Collections.Generic;
 using System.Linq;
 using CommunityToolkit.Mvvm.ComponentModel;
 using CommunityToolkit.Mvvm.Input;
+using STPViewer.Services;
 
 namespace STPViewer.ViewModels;
 
-/// <summary>快速列單一按鈕的顯示開關（選單「快速列 → 自訂按鈕」的 checkbox 項）</summary>
+/// <summary>Visibility toggle for one quick bar button.</summary>
 public partial class QuickBarItemViewModel : ObservableObject
 {
     public string Key { get; }
-    public string Label { get; }
+    public string Label => LocalizationService.Get(_labelKey);
+    private readonly string _labelKey;
     public bool Default { get; }
 
     [ObservableProperty]
@@ -19,57 +21,58 @@ public partial class QuickBarItemViewModel : ObservableObject
     public QuickBarItemViewModel(string key, string label, bool @default)
     {
         Key = key;
-        Label = label;
+        _labelKey = label;
         Default = @default;
         isChecked = @default;
     }
+
+    public void RefreshText() => OnPropertyChanged(nameof(Label));
 }
 
 /// <summary>
-/// 快速工具列自訂：所有功能都在選單列，快速列只放使用者勾選的常用按鈕。
-/// XAML 以索引子綁定：Visibility="{Binding QuickBar[Point].IsChecked, Converter=…}"。
-/// 勾選狀態隨 settings.json（QuickBarKeys）保存；null = 用預設。
+/// Quick bar button registry and saved visibility selections.
 /// </summary>
 public partial class QuickBarViewModel : ObservableObject
 {
-    /// <summary>註冊表 = 快速列順序 + 選單顯示名 + 是否預設顯示（一般 user 常用）</summary>
+    /// <summary>Button order, label key, and default visibility.</summary>
     private static readonly (string Key, string Label, bool Default)[] Registry =
     {
-        ("Import",       "📂 匯入",        true),
-        ("Recent",       "▾ 最近檔案",     true),
-        ("ZoomAll",      "🔍 全覽",        true),
-        ("ViewIso",      "視圖：等角",     true),
-        ("ViewFront",    "視圖：前",       false),
-        ("ViewTop",      "視圖：上",       false),
-        ("ViewRight",    "視圖：右",       false),
-        ("Ortho",        "正交投影",       true),
-        ("Point",        "📍 點",          true),
-        ("Distance",     "📏 距離",        true),
-        ("Edge",         "📐 邊",          false),
-        ("Face",         "⬛ 面",          false),
-        ("Circle",       "⭕ 圓",          true),
-        ("Angle",        "∠ 角度",         true),
-        ("FaceDistance", "⇔ 面距",         false),
-        ("Align",        "🎯 兩點對齊",    false),
-        ("Align3",       "🎯 三點對齊",    false),
-        ("RotateX",      "旋轉 ↻X",        false),
-        ("RotateY",      "旋轉 ↻Y",        false),
-        ("RotateZ",      "旋轉 ↻Z",        false),
-        ("Drag",         "🖐 拖曳",        false),
-        ("Gizmo",        "⊹ 操作器",       false),
-        ("Interference", "🧩 干涉",        true),
-        ("Section",      "✂ 剖面",         true),
-        ("Clear",        "🧹 清除量測",    true),
-        ("Unit",         "mm ⇄ in",        true),
-        ("ExportCsv",    "💾 匯出 CSV",    false),
-        ("Screenshot",   "📷 截圖",        false),
-        ("ExportStep",   "📤 匯出 STEP",   false),
-        ("ExportStl",    "📐 匯出 STL",    false),
+        ("Import",       "QuickBar.Import",        true),
+        ("Recent",       "QuickBar.Recent",        true),
+        ("ZoomAll",      "QuickBar.ZoomAll",       true),
+        ("ViewIso",      "QuickBar.ViewIso",       true),
+        ("ViewFront",    "QuickBar.ViewFront",     false),
+        ("ViewTop",      "QuickBar.ViewTop",       false),
+        ("ViewRight",    "QuickBar.ViewRight",     false),
+        ("Ortho",        "QuickBar.Ortho",         true),
+        ("Point",        "QuickBar.Point",         true),
+        ("Distance",     "QuickBar.Distance",      true),
+        ("Edge",         "QuickBar.Edge",          false),
+        ("Face",         "QuickBar.Face",          false),
+        ("Circle",       "QuickBar.Circle",        true),
+        ("Angle",        "QuickBar.Angle",         true),
+        ("FaceDistance", "QuickBar.FaceDistance",  false),
+        ("Align",        "QuickBar.Align",         false),
+        ("Align3",       "QuickBar.Align3",        false),
+        ("RotateX",      "QuickBar.RotateX",       false),
+        ("RotateY",      "QuickBar.RotateY",       false),
+        ("RotateZ",      "QuickBar.RotateZ",       false),
+        ("Drag",         "QuickBar.Drag",          false),
+        ("Gizmo",        "QuickBar.Gizmo",         false),
+        ("Interference", "QuickBar.Interference",  true),
+        ("Section",      "QuickBar.Section",       true),
+        ("Clear",        "QuickBar.Clear",         true),
+        ("Unit",         "QuickBar.Unit",          true),
+        ("ExportCsv",    "QuickBar.ExportCsv",     false),
+        ("Screenshot",   "QuickBar.Screenshot",    false),
+        ("ExportStep",   "QuickBar.ExportStep",    false),
+        ("ExportStl",    "QuickBar.ExportStl",     false),
+        ("Language",     "QuickBar.Language",      true),
     };
 
     private readonly Dictionary<string, QuickBarItemViewModel> _byKey;
 
-    /// <summary>依快速列順序的全部項目（選單自訂清單用）</summary>
+    /// <summary>All buttons in quick bar order.</summary>
     public IReadOnlyList<QuickBarItemViewModel> Items { get; }
 
     public QuickBarViewModel()
@@ -78,10 +81,10 @@ public partial class QuickBarViewModel : ObservableObject
         _byKey = Items.ToDictionary(i => i.Key);
     }
 
-    /// <summary>XAML 索引子綁定入口：QuickBar[Point].IsChecked</summary>
+    /// <summary>Indexer used by XAML visibility bindings.</summary>
     public QuickBarItemViewModel this[string key] => _byKey[key];
 
-    /// <summary>套用保存的勾選清單；null = 維持預設（含未知 key 容錯：新版本新增按鈕用預設值）</summary>
+    /// <summary>Loads saved visibility keys; null retains defaults.</summary>
     public void Load(List<string>? visibleKeys)
     {
         if (visibleKeys is null) return;
@@ -90,10 +93,16 @@ public partial class QuickBarViewModel : ObservableObject
             item.IsChecked = set.Contains(item.Key);
     }
 
-    /// <summary>目前勾選清單（存 settings.json）</summary>
+    /// <summary>Selected keys saved in settings.json.</summary>
     public List<string> ToKeys() =>
         Items.Where(i => i.IsChecked).Select(i => i.Key).ToList();
 
+    public void RefreshText()
+    {
+        foreach (QuickBarItemViewModel item in Items)
+            item.RefreshText();
+    }
+
     [RelayCommand]
     private void ResetDefaults()
     {
diff --git a/src/STPViewer/ViewModels/StlExportViewModel.cs b/src/STPViewer/ViewModels/StlExportViewModel.cs
index f99553b..0980533 100644
--- a/src/STPViewer/ViewModels/StlExportViewModel.cs
+++ b/src/STPViewer/ViewModels/StlExportViewModel.cs
@@ -5,18 +5,17 @@ using STPViewer.Services;
 namespace STPViewer.ViewModels;
 
 /// <summary>
-/// STL 匯出參數對話框的 ViewModel：範圍 / 格式 / 單位縮放 / 網格精度 + 即時摘要（三角形數、預估大小）。
-/// 對話框按「匯出」後由 MainViewModel.Export 讀取選項執行。
+/// Options and live size estimate for the STL export dialog.
 /// </summary>
 public partial class StlExportViewModel : ObservableObject
 {
-    /// <summary>可見（可匯出）檔案數</summary>
+    /// <summary>Number of visible files available for export.</summary>
     public int FileCount { get; }
 
-    /// <summary>目前顯示網格的三角形總數（精細/較粗會重新三角化，實際數量以結果為準）</summary>
+    /// <summary>Triangle count of the current display meshes.</summary>
     public long TriangleCount { get; }
 
-    /// <summary>是否有 B-rep 來源（全 STL/DXF 時精度選項無意義 → 停用）</summary>
+    /// <summary>Whether B-rep geometry is available for retessellation.</summary>
     public bool HasBrep { get; }
 
     public StlExportViewModel(int fileCount, long triangleCount, bool hasBrep)
@@ -26,17 +25,17 @@ public partial class StlExportViewModel : ObservableObject
         HasBrep = hasBrep;
     }
 
-    /// <summary>0 = 全部可見合併成單一 STL；1 = 每個可見檔案各一個 STL</summary>
+    /// <summary>0 = merged STL; 1 = one STL per visible file.</summary>
     [ObservableProperty]
     [NotifyPropertyChangedFor(nameof(Summary))]
     private int scopeIndex;
 
-    /// <summary>0 = Binary（建議，檔案小）；1 = ASCII（文字可讀，檔案大）</summary>
+    /// <summary>0 = binary; 1 = ASCII.</summary>
     [ObservableProperty]
     [NotifyPropertyChangedFor(nameof(Summary))]
     private int formatIndex;
 
-    /// <summary>0 = mm（1:1）；1 = inch（÷25.4）；2 = 自訂縮放</summary>
+    /// <summary>0 = millimeters; 1 = inches; 2 = custom scale.</summary>
     [ObservableProperty]
     [NotifyPropertyChangedFor(nameof(Summary))]
     [NotifyPropertyChangedFor(nameof(IsCustomScale))]
@@ -48,7 +47,7 @@ public partial class StlExportViewModel : ObservableObject
     [NotifyPropertyChangedFor(nameof(CanConfirm))]
     private string customScaleText = "1.0";
 
-    /// <summary>0 = 目前顯示網格；1 = 精細（B-rep 重新三角化）</summary>
+    /// <summary>0 = current mesh; 1 = finer B-rep tessellation.</summary>
     [ObservableProperty]
     [NotifyPropertyChangedFor(nameof(Summary))]
     private int qualityIndex;
@@ -59,7 +58,7 @@ public partial class StlExportViewModel : ObservableObject
     public bool PerFile => ScopeIndex == 1;
     public StlMeshQuality Quality => (StlMeshQuality)QualityIndex;
 
-    /// <summary>座標縮放；自訂值無效時回 null（擋確認）</summary>
+    /// <summary>Coordinate scale, or null for an invalid custom value.</summary>
     public double? Scale => UnitIndex switch
     {
         0 => 1.0,
@@ -77,9 +76,9 @@ public partial class StlExportViewModel : ObservableObject
             long est = StlExportService.EstimateBytes(TriangleCount, Ascii);
             string size = StlExportService.FormatBytes(est);
             string basis = QualityIndex == 0
-                ? $"預估 {size}"
-                : $"以目前網格預估 {size}（實際依重新三角化結果）";
-            return $"{FileCount} 個可見檔案 · {TriangleCount:N0} 三角形 · {basis}";
+                ? LocalizationService.Format("Ui.StlExport.EstimatedSize", size)
+                : LocalizationService.Format("Ui.StlExport.EstimatedSizeFine", size);
+            return LocalizationService.Format("Ui.StlExport.Summary", FileCount, TriangleCount.ToString("N0"), basis);
         }
     }
 }
diff --git a/src/STPViewer/i18n/en.json b/src/STPViewer/i18n/en.json
new file mode 100644
index 0000000..f21f6d8
--- /dev/null
+++ b/src/STPViewer/i18n/en.json
@@ -0,0 +1,417 @@
+{
+  "key": "English",
+  "data": {
+    "App.ErrorTitle": "STPViewer Error",
+    "App.NoRecentFiles": "(No recent files)",
+    "App.UnexpectedError": "An unexpected error interrupted the operation. The application will try to continue.\n\n{0}\n\nDetails: {1}",
+    "App.WindowTitle": "STPViewer V{0} — STP/STEP 3D Viewer",
+    "QuickBar.Align": "🎯 Two-point alignment",
+    "QuickBar.Align3": "🎯 Three-point alignment",
+    "QuickBar.Angle": "∠ Angle",
+    "QuickBar.Circle": "⭕ Circle",
+    "QuickBar.Clear": "🧹 Clear measurements",
+    "QuickBar.Distance": "📏 Distance",
+    "QuickBar.Drag": "🖐 Drag",
+    "QuickBar.Edge": "📐 Edge",
+    "QuickBar.ExportCsv": "💾 Export CSV",
+    "QuickBar.ExportStep": "📤 Export STEP",
+    "QuickBar.ExportStl": "📐 Export STL",
+    "QuickBar.Face": "⬛ Face",
+    "QuickBar.FaceDistance": "⇔ Face distance",
+    "QuickBar.Gizmo": "⊹ Gizmo",
+    "QuickBar.Import": "📂 Import",
+    "QuickBar.Interference": "🧩 Interference",
+    "QuickBar.Language": "Language",
+    "QuickBar.Ortho": "Orthographic projection",
+    "QuickBar.Point": "📍 Point",
+    "QuickBar.Recent": "▾ Recent files",
+    "QuickBar.RotateX": "Rotate ↻X",
+    "QuickBar.RotateY": "Rotate ↻Y",
+    "QuickBar.RotateZ": "Rotate ↻Z",
+    "QuickBar.Screenshot": "📷 Screenshot",
+    "QuickBar.Section": "✂ Section",
+    "QuickBar.Unit": "mm ⇄ in",
+    "QuickBar.ViewFront": "View: Front",
+    "QuickBar.ViewIso": "View: Isometric",
+    "QuickBar.ViewRight": "View: Right",
+    "QuickBar.ViewTop": "View: Top",
+    "QuickBar.ZoomAll": "🔍 Zoom all",
+    "Runtime.Align3Completed": "Aligned “{0}” using three points (rotation + translation; point 1 matched exactly, measurements cleared)",
+    "Runtime.Align3Failed": "Three-point alignment failed (degenerate points); select new points",
+    "Runtime.Align3OtherFile": "Target points must be on another file",
+    "Runtime.Align3SameSource": "All three source points must be on one file (moving: {0})",
+    "Runtime.Align3SourceCollinear": "The three points are collinear; choose a different third point",
+    "Runtime.Align3SourceComplete": "Three source points selected — select matching point 1/3 on the target file",
+    "Runtime.Align3SourcePoint": "Source point {0}/3 — keep selecting points on “{1}”",
+    "Runtime.Align3TargetCollinear": "Target points are collinear; choose a different third point",
+    "Runtime.Align3TargetPoint": "Target point {0}/3 — select the next matching point",
+    "Runtime.AlignMoved": "Moved “{0}” Δ({1:F3}, {2:F3}, {3:F3}) mm (measurements cleared; use face distance or interference to check fit)",
+    "Runtime.AlignMoving": "Moving “{0}” — select a target point on another file",
+    "Runtime.AlignOtherFile": "The target point must be on another file",
+    "Runtime.AllVisible": "All shown",
+    "Runtime.AngleDetail": "Angle = {0:F2}° (supplement {1:F2}°)\nDirection 1: {2} ({3:F3}, {4:F3}, {5:F3})\nDirection 2: {6} ({7:F3}, {8:F3}, {9:F3})\n(Face angles use normals; see supplement for the complementary angle)",
+    "Runtime.AngleFirstDirection": "First direction selected ({0}) — select another face or edge",
+    "Runtime.ArcLength": "Arc length",
+    "Runtime.Axis": "{0} axis",
+    "Runtime.CircleDetail": "Diameter = {0}\nRadius = {1}\n{2} = {3}\nCenter {4}",
+    "Runtime.Circumference": "Circumference",
+    "Runtime.ComponentName": "Component",
+    "Runtime.ConicalSurface": "Conical surface",
+    "Runtime.CsvEmpty": "No measurements to export",
+    "Runtime.CsvExported": "Exported {0} measurements → {1}",
+    "Runtime.CsvFilter": "CSV files (*.csv)|*.csv",
+    "Runtime.CsvHeader": "Label,Type,Details",
+    "Runtime.CsvTitle": "Export measurements",
+    "Runtime.CurveDetail": "Curve length = {0}\nType = {1}",
+    "Runtime.CurveName": "Curve",
+    "Runtime.CustomPlane": "custom plane",
+    "Runtime.CylinderSurface": "Type = cylindrical surface\nRadius = {0}\nAxis ({1:F3}, {2:F3}, {3:F3})",
+    "Runtime.DirectionEdge": "Edge direction",
+    "Runtime.DirectionFace": "Face normal",
+    "Runtime.DirectionMeshFace": "Face normal (mesh)",
+    "Runtime.DistanceDetail": "Distance = {0}\nΔX = {1}\nΔY = {2}\nΔZ = {3}\nP1 {4}\nP2 {5}",
+    "Runtime.DistanceFirstPoint": "First point ({0:F2}, {1:F2}, {2:F2}) — select the second point",
+    "Runtime.Dragged": "Dragged “{0}” Δ({1:F2}, {2:F2}, {3:F2}) mm (use interference check to verify)",
+    "Runtime.Dragging": "Dragging “{0}”… (release to place)",
+    "Runtime.DxfParseFailed": "Could not parse DXF file",
+    "Runtime.ExtrusionSurface": "Extruded surface",
+    "Runtime.FaceDetail": "Area ≈ {0} (mesh approximation)\n{1}\nTriangles = {2:N0}",
+    "Runtime.FaceDistanceDetail": "Minimum distance ≈ {0} (mesh approximation)\nΔX = {1}\nΔY = {2}\nΔZ = {3}\nPoint 1 {4}\nPoint 2 {5}",
+    "Runtime.FaceDistanceFirstFace": "First face selected — select another face",
+    "Runtime.FaceName": "Face",
+    "Runtime.FileNotFound": "File not found",
+    "Runtime.GapLabel": "gap {0}",
+    "Runtime.GeometryProcessed": "Geometry processed in {0:N0} ms (triangulation {1:N0} ms, edge sampling {2:N0} ms{3})",
+    "Runtime.GizmoApplied": "Applied gizmo transform to “{0}” (use interference check to verify)",
+    "Runtime.GizmoHint": "Gizmo: drag an arrow to move “{0}” along an axis or a ring to rotate; release to place",
+    "Runtime.GizmoSelectFile": "Gizmo: select a file in the tree first",
+    "Runtime.ImportBusy": "Busy importing or calculating; please wait",
+    "Runtime.ImportCompleted": "Import complete: {0} succeeded{1}",
+    "Runtime.ImportFailed": "Import failed: {0} — {1}",
+    "Runtime.ImportFailedCount": ", {0} failed",
+    "Runtime.ImportFailedTitle": "Import failed",
+    "Runtime.ImportFilter": "CAD files (*.stp;*.step;*.stl;*.dxf)|*.stp;*.step;*.stl;*.dxf|STEP (*.stp;*.step)|*.stp;*.step|STL (*.stl)|*.stl|DXF (*.dxf)|*.dxf|All files (*.*)|*.*",
+    "Runtime.ImportProgress": "Importing {0}: {1}",
+    "Runtime.ImportTitle": "Import CAD files (multiple selection)",
+    "Runtime.Importing": "Importing: {0}…",
+    "Runtime.InterferenceChecking": "Checking interference (pair {0}): {1} ⟷ {2}…",
+    "Runtime.InterferenceClearDetail": "{0} ⟷ {1} do not intersect\nMinimum gap ≈ {2} (mesh approximation)\nGap ≈ 0 means contact (match)\nPoint 1 {3}\nPoint 2 {4}",
+    "Runtime.InterferenceClearTitle": "🧩 No interference  gap ≈ {0}",
+    "Runtime.InterferenceCompleted": "Interference check complete: {0} pairs, {1} intersecting",
+    "Runtime.InterferenceFailed": "Interference check failed: {0}",
+    "Runtime.InterferenceHitDetail": "Parts intersect (no match)\nIntersecting triangle pairs = {0:N0}\nRed lines = intersection curves ({1:N0} segments)\n(Coplanar contact is not counted as interference)",
+    "Runtime.InterferenceHitTitle": "🧩 Interference! {0} ⟷ {1}",
+    "Runtime.InterferenceLabel": "Interference",
+    "Runtime.InterferenceNeedTwo": "Interference check needs at least two visible files ({0} now); select them in the tree",
+    "Runtime.Isolated": "Showing only “{0}” (tree context menu → Show all to restore)",
+    "Runtime.KindAlign": "Align",
+    "Runtime.KindAlign3": "Three-point align",
+    "Runtime.KindAngle": "Angle",
+    "Runtime.KindCircle": "Circle",
+    "Runtime.KindDistance": "Distance",
+    "Runtime.KindDrag": "Drag",
+    "Runtime.KindEdge": "Edge",
+    "Runtime.KindFace": "Face",
+    "Runtime.KindFaceDistance": "Face distance",
+    "Runtime.KindInterference": "Interference",
+    "Runtime.KindNone": "None",
+    "Runtime.KindPoint": "Point",
+    "Runtime.KindVolume": "Volume",
+    "Runtime.LineDetail": "Length = {0}\nΔX = {1}  ΔY = {2}  ΔZ = {3}\nStart {4}\nEnd {5}",
+    "Runtime.MeasureFailed": "Measurement failed: {0}",
+    "Runtime.MeasurementStartCancelled": "Current measurement start cancelled (press Esc again to leave measurement mode)",
+    "Runtime.MeasurementsCleared": "All measurements cleared",
+    "Runtime.MeshMeasurementLimited": "This model has no B-rep (STL/mesh); only point, distance, angle and face distance measurements are available",
+    "Runtime.MeshName": "Mesh",
+    "Runtime.MeshNameNumbered": "Mesh {0}",
+    "Runtime.MeshSurface": "Type = mesh (no B-rep)",
+    "Runtime.ModeAlign": "Two-point align: select a point on the part to move, then a target point (translation only; measurements cleared)",
+    "Runtime.ModeAlign3": "Three-point align: select three feature points on the file to move, then three matching points on the target file",
+    "Runtime.ModeAngle": "Angle measurement: select the first face (or near a straight edge)",
+    "Runtime.ModeBrowse": "Browse mode (right drag to orbit, wheel to zoom, middle drag or Shift+left drag to pan)",
+    "Runtime.ModeCircle": "Circle measurement: click near a circular edge or hole wall",
+    "Runtime.ModeDistance": "Distance measurement: select the first point",
+    "Runtime.ModeDrag": "Drag mode: hold left mouse button to drag a part in the screen plane, release to place it; rotate the view to change depth",
+    "Runtime.ModeEdge": "Edge measurement: click near an edge",
+    "Runtime.ModeFace": "Face measurement: click a face",
+    "Runtime.ModeFaceDistance": "Face distance measurement: select the first face",
+    "Runtime.ModePoint": "Point measurement: click a model surface (snaps to nearby vertices)",
+    "Runtime.NoBrep": " · No B-rep",
+    "Runtime.NoCircularEdge": "This face has no circular edge (click near a hole wall or circular edge)",
+    "Runtime.NoGeometry": "File contains no displayable geometry",
+    "Runtime.NoMeasurableEdge": "This face has no measurable edge",
+    "Runtime.NoSurfaceHit": "No model surface hit",
+    "Runtime.NodeStats": "{0} solids · {1} faces · {2:N0} △",
+    "Runtime.NurbsSurface": "NURBS surface",
+    "Runtime.Orthographic": "Orthographic projection (parallel view for checking dimensions)",
+    "Runtime.OutlineSize": "\nBounds {0}",
+    "Runtime.ParsingStep": "Parsing STEP (large files may take several minutes)…",
+    "Runtime.ParsingStl": "Parsing STL triangles…",
+    "Runtime.Perspective": "Perspective projection",
+    "Runtime.PlaneSurface": "Type = plane\nNormal ({0:F3}, {1:F3}, {2:F3})",
+    "Runtime.Ready": "Ready — import STP/STEP/STL/DXF (or drag and drop). Right drag to orbit, wheel to zoom, middle drag or Shift+left drag to pan",
+    "Runtime.Removed": "Removed: {0}",
+    "Runtime.RetriedFaces": ", recovered {0} faces",
+    "Runtime.Reversed": " (reversed)",
+    "Runtime.RevolutionSurface": "Surface of revolution",
+    "Runtime.RootNotFound": "Could not find this part's file",
+    "Runtime.RotateSelectFile": "Select a file to rotate in the tree first",
+    "Runtime.Rotated": "Rotated “{0}” +90° around {1} axis (click again to continue)",
+    "Runtime.SameFace": "The same face was selected twice; select another face",
+    "Runtime.ScreenshotFilter": "PNG images (*.png)|*.png",
+    "Runtime.ScreenshotSaved": "Screenshot saved → {0}",
+    "Runtime.ScreenshotTitle": "Save view screenshot",
+    "Runtime.SectionCancelled": "3-point section definition cancelled",
+    "Runtime.SectionClosed": "Section closed",
+    "Runtime.SectionCollinear": "3-point section: points are collinear; choose a different third point",
+    "Runtime.SectionDefined": "3-point section: plane defined (normal {0:F2}, {1:F2}, {2:F2}) — move the position slider to scan",
+    "Runtime.SectionDegenerate": "3-point section: points are degenerate; select again",
+    "Runtime.SectionNoHit": "3-point section: no model surface hit ({0}/3 points selected, Esc to cancel)",
+    "Runtime.SectionPickPrompt": "3-point section: click three points on the model to define the cutting plane (Esc to cancel)",
+    "Runtime.SectionPicked": "3-point section: {0}/3 points selected",
+    "Runtime.SectionStatus": "Section: {0} {1:F0}%{2}",
+    "Runtime.ShellName": "Shell",
+    "Runtime.SolidName": "Solid",
+    "Runtime.SphericalSurface": "Spherical surface",
+    "Runtime.StepExportEmpty": "No B-rep geometry to export (STEP supports Solid/Shell; select a STEP file to export)",
+    "Runtime.StepExportFailed": "STEP export failed: {0}",
+    "Runtime.StepExportFilter": "STEP files (*.stp)|*.stp|STEP files (*.step)|*.step",
+    "Runtime.StepExportTitle": "Export current scene as STEP (parts at current aligned positions)",
+    "Runtime.StepExported": "Exported STEP ({0} solids at current positions) → {1}",
+    "Runtime.StepParseFailed": "CADability could not parse this STEP file",
+    "Runtime.StepParsed": "STEP parsed in {0:N0} ms",
+    "Runtime.StlExportEmpty": "No meshes to export (select at least one file with a solid mesh)",
+    "Runtime.StlExportFailed": "STL export failed: {0}",
+    "Runtime.StlExportFilter": "STL files (*.stl)|*.stl",
+    "Runtime.StlExportMergedTitle": "Export STL (merged into one file)",
+    "Runtime.StlExportPerFileTitle": "Export STL (one per file; use this as the base filename)",
+    "Runtime.StlExportedMany": "Exported {0} STL files ({1:N0} triangles total) → {2}",
+    "Runtime.StlExportedOne": "Exported STL ({0:N0} triangles) → {1}",
+    "Runtime.StlExporting": "Exporting STL…",
+    "Runtime.StlNoTriangles": "STL file contains no triangles",
+    "Runtime.StlParsed": "STL parsed in {0:N0} ms ({1} meshes)",
+    "Runtime.StlRetriangulating": "Retriangulating and exporting STL… (large assemblies take time)",
+    "Runtime.SurfaceType": "Type = {0}",
+    "Runtime.ToroidalSurface": "Toroidal surface",
+    "Runtime.Triangulating": "Triangulating {0} parts in parallel…",
+    "Runtime.UnitInch": "Display unit: inch",
+    "Runtime.UnitMillimeter": "Display unit: mm",
+    "Runtime.UnsupportedFormat": "Unsupported format (.stp / .step / .stl / .dxf supported; CADability has no IGES reader)",
+    "Runtime.View": "View: {0}",
+    "Runtime.ViewBack": "Back",
+    "Runtime.ViewBottom": "Bottom",
+    "Runtime.ViewFront": "Front",
+    "Runtime.ViewIso": "Isometric",
+    "Runtime.ViewLeft": "Left",
+    "Runtime.ViewRight": "Right",
+    "Runtime.ViewTop": "Top",
+    "Runtime.VisibilityInverted": "Visibility inverted",
+    "Runtime.VolumeDetail": "Volume ≈ {0} (mesh approximation)\nCentroid {1}\nBounds (AABB) {2} × {3} × {4} {5}",
+    "Runtime.VolumeNoMesh": "“{0}” has no face mesh for volume calculation (wireframe has no volume)",
+    "Runtime.VolumeOpenMesh": "“{0}” is an open mesh; volume cannot be calculated reliably",
+    "Ui.About.Changelog": "📋  Release History",
+    "Ui.About.Close": "Close",
+    "Ui.About.Description": "STP / STEP 3D Viewer. Open, measure, align, check interference, section, and export without starting a full CAD application.",
+    "Ui.About.Developer": "👤  Developer",
+    "Ui.About.Email": "Email",
+    "Ui.About.Name": "Name",
+    "Ui.About.Release010.Change1": "• STEP, STL, and DXF import with an assembly tree; point, distance, edge, face, circle, angle, and face-distance measurement; alignment, interference checking, sections, units, CSV, and screenshots.",
+    "Ui.About.Release010.Title": "First Release",
+    "Ui.About.Release020.Change1": "• Hold the left mouse button on a part to drag it into position.",
+    "Ui.About.Release020.Change2": "• Version 0.2.1 fixed a crash after clicking a dragged part.",
+    "Ui.About.Release020.Title": "Drag Mode",
+    "Ui.About.Release030.Change1": "• Select a model and use XYZ arrows to move it along an axis or rings to rotate it by any angle.",
+    "Ui.About.Release030.Title": "3-Axis Gizmo",
+    "Ui.About.Release031.Change1": "• The 3-axis gizmo stays above the model and remains accessible from any angle.",
+    "Ui.About.Release031.Title": "Gizmo Always Visible",
+    "Ui.About.Release032.Change1": "• Rotating a large assembly remains smooth while measuring.",
+    "Ui.About.Release032.Title": "Smooth Measurement of Large Assemblies",
+    "Ui.About.Release040.Change1": "• Moving the section slider on a large file no longer freezes the window.",
+    "Ui.About.Release040.Change2": "• Placement after dragging or using the gizmo is much faster.",
+    "Ui.About.Release040.Change3": "• Errors now show a message and let the application keep running.",
+    "Ui.About.Release040.Title": "Faster and More Reliable",
+    "Ui.About.Release050.Change1": "• Distance measurement snaps to the center of a circular edge, making hole pitch easy to measure.",
+    "Ui.About.Release050.Change2": "• Measurement shortcuts: P point, D distance, E edge, F face, C circle, A angle, M face distance; Esc cancels.",
+    "Ui.About.Release050.Change3": "• Search part names in the model tree; right-click to isolate a node or measure volume and centroid.",
+    "Ui.About.Release050.Change4": "• Standard views and orthographic projection make dimensions easier to inspect without perspective distortion.",
+    "Ui.About.Release050.Change5": "• A three-point section mode cuts along any plane defined by three points on the model.",
+    "Ui.About.Release050.Change6": "• Export aligned parts to a new STEP file for use in CAD.",
+    "Ui.About.Release050.Change7": "• Window size, unit preferences, and the ten most recently opened files are remembered.",
+    "Ui.About.Release050.Title": "Major Improvements to Measurement, Views, and the Model Tree",
+    "Ui.About.Release060.Change1": "• Export visible parts, including their aligned and rotated positions, to STL for 3D printing or other software.",
+    "Ui.About.Release060.Change2": "• Choose one merged file or one file per model, Binary or ASCII, mm or inches, and mesh quality before exporting.",
+    "Ui.About.Release060.Change3": "• The settings dialog shows triangle count and estimated file size immediately.",
+    "Ui.About.Release060.Title": "Export STL",
+    "Ui.About.Release070.Change1": "• A new menu bar groups all features under File, View, Measure, Transform, and Tools.",
+    "Ui.About.Release070.Change2": "• Choose your favorite Quick Bar buttons from Quick Bar → Customize Buttons; your selection is saved.",
+    "Ui.About.Release070.Change3": "• Section controls appear only when section view is active.",
+    "Ui.About.Release070.Change4": "• A new About window shows the release history.",
+    "Ui.About.Release070.Title": "Redesigned Interface with Menus and a Customizable Quick Bar",
+    "Ui.About.Release071.Change1": "• Large STL mesh files with millions of triangles now open almost instantly instead of taking several minutes.",
+    "Ui.About.Release071.Change2": "• For example, a 75 MB STL with 1.5 million triangles now appears in under a second.",
+    "Ui.About.Release071.Title": "Open Large STL Files in Seconds",
+    "Ui.About.Technology": ".NET 8 · WPF · C#; CADability (STEP / B-rep geometry); HelixToolkit (3D display and camera)",
+    "Ui.About.TechnologyTitle": "🔧  Technology",
+    "Ui.About.Title": "About STPViewer",
+    "Ui.Language": "Language",
+    "Ui.Main.3AxisGizmo": "⊹ 3-Axis Gizmo",
+    "Ui.Main.3AxisGizmoUseXYZArrows": "3-axis gizmo: use XYZ arrows to move and rings to rotate the selected model; release to place it",
+    "Ui.Main.3Point": "🎯 3-Point",
+    "Ui.Main.3Points": "3 Points",
+    "Ui.Main.Align": "🎯 Align",
+    "Ui.Main.Angle": "∠ Angle",
+    "Ui.Main.AngleBetweenFacesStraightEdgesShortcut": "Angle between faces or straight edges — shortcut A",
+    "Ui.Main.AngleBetweenTwoFacesStraightEdges": "Angle between two faces or straight edges",
+    "Ui.Main.ApplicationInformationReleaseHistory": "Application information and release history",
+    "Ui.Main.AreaSurfaceTypeNormalVector": "Area, surface type, and normal vector",
+    "Ui.Main.AreaSurfaceTypeNormalVectorShortcut": "Area, surface type, and normal vector — shortcut F",
+    "Ui.Main.Capture": "📷 Capture",
+    "Ui.Main.CenterRadiusDiameterCircumference": "Center, radius, diameter, and circumference",
+    "Ui.Main.CenterRadiusDiameterCircumferenceShortcutC": "Center, radius, diameter, and circumference — shortcut C",
+    "Ui.Main.CheckButtonsShowQuickBarSaved": "Check the buttons to show on the Quick Bar (saved in settings)",
+    "Ui.Main.CheckVisibleModelPairsIntersectionsReport": "Check visible model pairs for intersections; report the smallest gap when none intersect",
+    "Ui.Main.ChooseScopeFormatUnitsMeshQuality": "Choose scope, format, units, and mesh quality before exporting",
+    "Ui.Main.Circle": "⭕ Circle",
+    "Ui.Main.Clear": "🧹 Clear",
+    "Ui.Main.ClearAllMeasurements": "🧹 Clear All Measurements",
+    "Ui.Main.ClearAllMeasurementsMarkersEscCancels": "Clear all measurements and markers (Esc cancels the current measurement or mode)",
+    "Ui.Main.ClickChangeColorIncludingChildNodes": "Click to change color (including child nodes)",
+    "Ui.Main.Close": "✕ Close",
+    "Ui.Main.CloseSectionView": "Close section view",
+    "Ui.Main.CustomizeButtons": "Customize Buttons",
+    "Ui.Main.DeleteThisMeasurement": "Delete this measurement",
+    "Ui.Main.DisplayInchesMm": "Display in Inches (mm ⇄ in)",
+    "Ui.Main.Distance": "📏 Distance",
+    "Ui.Main.DistanceXYZCircleCenterSnappingHole": "Distance and ΔXYZ with circle-center snapping for hole pitch — shortcut D",
+    "Ui.Main.DistanceXYZCircularEdgesSnapCenters": "Distance and ΔXYZ; circular edges snap to centers for hole pitch measurement",
+    "Ui.Main.Drag": "🖐 Drag",
+    "Ui.Main.DragMode": "🖐 Drag Mode",
+    "Ui.Main.DragModeHoldLeftMouseButton": "Drag mode: hold the left mouse button to move a part in the screen plane; rotate the view to move in depth",
+    "Ui.Main.DragResizePanel": "Drag to resize the panel",
+    "Ui.Main.Edge": "📐 Edge",
+    "Ui.Main.EdgeLength": "📐 Edge Length",
+    "Ui.Main.Edges": "Edges",
+    "Ui.Main.EscCancelsCurrentMeasurementExitsMode": "Esc cancels the current measurement or exits the mode",
+    "Ui.Main.ExistingMeasurementsUpdateImmediatelyValuesStored": "Existing measurements update immediately; values are stored internally in mm",
+    "Ui.Main.ExportMeasurementResultsCSV": "Export measurement results as CSV",
+    "Ui.Main.ExportMeasurementsCSV": "💾 Export Measurements as CSV…",
+    "Ui.Main.ExportSTEP": "📤 Export STEP…",
+    "Ui.Main.ExportSTL": "📐 Export STL…",
+    "Ui.Main.ExportStepTooltip": "Export visible models at their current positions to a new STEP file; source files stay unchanged",
+    "Ui.Main.Face": "⬛ Face",
+    "Ui.Main.FaceDistance": "⇔ Face Distance",
+    "Ui.Main.FileF": "File (_F)",
+    "Ui.Main.FilterAssemblyTreeByNameDoes": "Filter assembly tree by name (does not change 3D visibility; clear to show all)",
+    "Ui.Main.Fit": "🔍 Fit",
+    "Ui.Main.FitAllModelsView": "Fit all models in view",
+    "Ui.Main.Flip": "Flip",
+    "Ui.Main.Front": "Front",
+    "Ui.Main.FrontView": "Front View",
+    "Ui.Main.FrontViewLookAlongYZ": "Front view (look along −Y, Z up)",
+    "Ui.Main.Gizmo": "⊹ Gizmo",
+    "Ui.Main.HelpH": "Help (_H)",
+    "Ui.Main.HoldLeftMouseButtonMovePart": "Hold the left mouse button to move a part in the screen plane; release to place it",
+    "Ui.Main.IAboutSTPViewer": "ℹ About STPViewer…",
+    "Ui.Main.ImportSTPSTEPSTLDXFFiles": "Import STP/STEP/STL/DXF files (select multiple or drag files into the window)",
+    "Ui.Main.Interference": "🧩 Interference",
+    "Ui.Main.InterferenceCheck": "🧩 Interference Check",
+    "Ui.Main.InterferenceCheckTestVisibleModelPairs": "Interference check: test visible model pairs for intersections or contact; report the smallest gap",
+    "Ui.Main.InvertVisibility": "🔄 Invert Visibility",
+    "Ui.Main.Iso": "Iso",
+    "Ui.Main.IsometricView": "Isometric View",
+    "Ui.Main.LookAlongXZUp": "Look along +X, with Z up",
+    "Ui.Main.LookAlongYZUp": "Look along −Y, with Z up",
+    "Ui.Main.LookDownFromZ": "Look down from +Z",
+    "Ui.Main.MeasureM": "Measure (_M)",
+    "Ui.Main.MeasurePointCoordinatesSnapsVerticesCircle": "Measure point coordinates (snaps to vertices and circle centers)",
+    "Ui.Main.MeasureStraightCurvedCircularEdgeLengths": "Measure straight, curved, and circular edge lengths",
+    "Ui.Main.MeasureVolumeCentroid": "⚖ Measure Volume / Centroid",
+    "Ui.Main.Measurements": "Measurements",
+    "Ui.Main.MenuImport": "📂 Import…",
+    "Ui.Main.ModelsAssemblyTree": "Models / Assembly Tree",
+    "Ui.Main.Ortho": "Ortho",
+    "Ui.Main.OrthographicProjection": "Orthographic Projection",
+    "Ui.Main.OrthographicProjectionAvoidsPerspectiveDistortionClick": "Orthographic projection avoids perspective distortion; click again for perspective",
+    "Ui.Main.ParallelProjectionAvoidsPerspectiveDistortionUncheck": "Parallel projection avoids perspective distortion; uncheck for perspective view",
+    "Ui.Main.PickPointPartMoveThenPick": "Pick a point on the part to move, then pick the target point",
+    "Ui.Main.PickThreePointsMovingModelThen": "Pick three points on the moving model, then three matching points on the target in the same order",
+    "Ui.Main.Point": "📍 Point",
+    "Ui.Main.PointCoordinates": "📍 Point Coordinates",
+    "Ui.Main.PointCoordinatesVertexCircleCenterSnapping": "Point coordinates with vertex/circle-center snapping — shortcut P",
+    "Ui.Main.QuickBarQ": "Quick Bar (_Q)",
+    "Ui.Main.RecentFiles": "Recent Files",
+    "Ui.Main.RecentlyOpenedFiles": "Recently opened files",
+    "Ui.Main.RemoveThisFile": "Remove this file",
+    "Ui.Main.RestoreDefaultButtons": "Restore Default Buttons",
+    "Ui.Main.Right": "Right",
+    "Ui.Main.RightView": "Right View",
+    "Ui.Main.RightViewLookAlongXZ": "Right view (look along +X, Z up)",
+    "Ui.Main.Rotate90AroundX": "↻ Rotate +90° Around X",
+    "Ui.Main.Rotate90AroundY": "↻ Rotate +90° Around Y",
+    "Ui.Main.Rotate90AroundZ": "↻ Rotate +90° Around Z",
+    "Ui.Main.RotateModelSelectedTree90Around": "Rotate the model selected in the tree +90° around X",
+    "Ui.Main.RotateModelSelectedTreeAroundIts": "Rotate the model selected in the tree around its center",
+    "Ui.Main.RotateSelectedModel90AroundY": "Rotate the selected model +90° around Y",
+    "Ui.Main.RotateSelectedModel90AroundZ": "Rotate the selected model +90° around Z",
+    "Ui.Main.SavePNGScreenshot3DView2": "Save a PNG screenshot of the 3D view at 2× resolution",
+    "Ui.Main.SaveViewPNG": "📷 Save View as PNG…",
+    "Ui.Main.SectionAxis3PointsDefineAn": "Section axis (3 points define an arbitrary plane on the model)",
+    "Ui.Main.SectionLabel": "✂ Section:",
+    "Ui.Main.SectionPosition0100EnterValue": "Section position (0–100%; enter a value and leave the field to apply)",
+    "Ui.Main.SectionPositionAlongNormal": "Section position (% along normal)",
+    "Ui.Main.SectionView": "✂ Section View",
+    "Ui.Main.ShortestDistanceBetweenFacesMeshApproximation": "Shortest distance between faces (mesh approximation)",
+    "Ui.Main.ShortestFaceDistanceMeshApproximationShortcut": "Shortest face distance (mesh approximation) — shortcut M",
+    "Ui.Main.ShowAll": "☀ Show All",
+    "Ui.Main.ShowHideIncludingChildNodes": "Show / hide (including child nodes)",
+    "Ui.Main.ShowOnlyThisNode": "👁 Show Only This Node",
+    "Ui.Main.ShowOutlineEdgesManyEdgesCan": "Show outline edges (many edges can slow view rotation)",
+    "Ui.Main.ShowSectionControlsAxisPositionDirection": "Show section controls for axis, position, and direction",
+    "Ui.Main.ShowXYZArrowsRotationRingsSelected": "Show XYZ arrows and rotation rings for the selected model; release to place it",
+    "Ui.Main.StraightCurvedCircularEdgeLengthShortcut": "Straight, curved, or circular edge length — shortcut E",
+    "Ui.Main.SwitchDisplayUnitsBetweenMmInches": "Switch display units between mm and inches (existing measurements update)",
+    "Ui.Main.SwitchRetainedSide": "Switch the retained side",
+    "Ui.Main.ThreePointAlignmentPickThreePoints": "Three-point alignment: pick three points on the moving model, then matching points on the target",
+    "Ui.Main.ThreePointAlignmentRotateTranslate": "🎯 Three-Point Alignment (Rotate + Translate)",
+    "Ui.Main.ToggleSectionViewItsControls": "Toggle section view and its controls",
+    "Ui.Main.ToolbarExportStepTooltip": "Export visible models at their current positions to STEP for CAD; source files stay unchanged",
+    "Ui.Main.ToolbarExportStlTooltip": "Export visible models at their current positions to STL; choose scope, format, units, and quality first",
+    "Ui.Main.ToolbarImport": "📂 Import",
+    "Ui.Main.ToolbarSection": "✂ Section",
+    "Ui.Main.ToolsL": "Tools (_L)",
+    "Ui.Main.Top": "Top",
+    "Ui.Main.TopView": "Top View",
+    "Ui.Main.TopViewLookDownFromZ": "Top view (look down from +Z)",
+    "Ui.Main.TransformT": "Transform (_T)",
+    "Ui.Main.TwoPointAlignmentPickPointMoving": "Two-point alignment: pick a point on the moving part, then the target point",
+    "Ui.Main.TwoPointAlignmentTranslate": "🎯 Two-Point Alignment (Translate)",
+    "Ui.Main.TwoPointDistance": "📏 Two-Point Distance",
+    "Ui.Main.ViewV": "View (_V)",
+    "Ui.Main.WindowTitle": "STPViewer — STP/STEP 3D Viewer",
+    "Ui.Main.ZoomFit": "🔍 Zoom to Fit",
+    "Ui.Main.ZoomThisNode": "Zoom to this node",
+    "Ui.StlExport.Cancel": "Cancel",
+    "Ui.StlExport.CustomScaleTooltip": "Multiply coordinates by this factor (for example, 0.001 converts mm to m)",
+    "Ui.StlExport.EstimatedSize": "Estimated {0}",
+    "Ui.StlExport.EstimatedSizeFine": "Current mesh estimate {0} (actual size depends on re-triangulation)",
+    "Ui.StlExport.Export": "Export…",
+    "Ui.StlExport.Format": "Format",
+    "Ui.StlExport.FormatAscii": "ASCII (readable text; about 4× larger)",
+    "Ui.StlExport.FormatBinary": "Binary (recommended; smaller file)",
+    "Ui.StlExport.MeshQuality": "Mesh quality",
+    "Ui.StlExport.QualityCurrent": "Current display mesh (fast; matches the view)",
+    "Ui.StlExport.QualityFine": "Fine — re-triangulate for smoother surfaces (slower; larger file)",
+    "Ui.StlExport.QualityTooltip": "Fine quality re-triangulates STEP B-rep geometry; STL/DXF keeps the current mesh. Large assemblies take time",
+    "Ui.StlExport.Scope": "Export scope",
+    "Ui.StlExport.ScopeMerge": "All visible models → one STL",
+    "Ui.StlExport.ScopePerFile": "Each visible model → separate STL",
+    "Ui.StlExport.ScopeTooltip": "STL has no assembly structure; merge puts all visible parts in one file",
+    "Ui.StlExport.Summary": "{0} visible models · {1} triangles · {2}",
+    "Ui.StlExport.Title": "Export STL — Settings",
+    "Ui.StlExport.UnitCustom": "Custom scale factor…",
+    "Ui.StlExport.UnitInch": "inch (coordinates ÷ 25.4)",
+    "Ui.StlExport.UnitMillimeter": "mm (1:1; default)",
+    "Ui.StlExport.UnitScale": "Unit scale",
+    "Ui.StlExport.UnitTooltip": "STL files have no units; internal geometry is in mm, and inches divide coordinates by 25.4"
+  }
+}
diff --git a/src/STPViewer/i18n/zh_cn.json b/src/STPViewer/i18n/zh_cn.json
new file mode 100644
index 0000000..f9cda16
--- /dev/null
+++ b/src/STPViewer/i18n/zh_cn.json
@@ -0,0 +1,417 @@
+{
+  "key": "简体中文",
+  "data": {
+    "App.ErrorTitle": "STPViewer 错误",
+    "App.NoRecentFiles": "（没有最近打开的文件）",
+    "App.UnexpectedError": "发生意外错误，操作已中止（程序将尝试继续运行）。\n\n{0}\n\n详细记录：{1}",
+    "App.WindowTitle": "STPViewer V{0} — STP/STEP 3D 查看器",
+    "QuickBar.Align": "🎯 两点对齐",
+    "QuickBar.Align3": "🎯 三点对齐",
+    "QuickBar.Angle": "∠ 角度",
+    "QuickBar.Circle": "⭕ 圆",
+    "QuickBar.Clear": "🧹 清除测量",
+    "QuickBar.Distance": "📏 距离",
+    "QuickBar.Drag": "🖐 拖动",
+    "QuickBar.Edge": "📐 边",
+    "QuickBar.ExportCsv": "💾 导出 CSV",
+    "QuickBar.ExportStep": "📤 导出 STEP",
+    "QuickBar.ExportStl": "📐 导出 STL",
+    "QuickBar.Face": "⬛ 面",
+    "QuickBar.FaceDistance": "⇔ 面距",
+    "QuickBar.Gizmo": "⊹ 操作器",
+    "QuickBar.Import": "📂 导入",
+    "QuickBar.Interference": "🧩 干涉",
+    "QuickBar.Language": "语言",
+    "QuickBar.Ortho": "正交投影",
+    "QuickBar.Point": "📍 点",
+    "QuickBar.Recent": "▾ 最近文件",
+    "QuickBar.RotateX": "旋转 ↻X",
+    "QuickBar.RotateY": "旋转 ↻Y",
+    "QuickBar.RotateZ": "旋转 ↻Z",
+    "QuickBar.Screenshot": "📷 截图",
+    "QuickBar.Section": "✂ 剖面",
+    "QuickBar.Unit": "mm ⇄ in",
+    "QuickBar.ViewFront": "视图：前",
+    "QuickBar.ViewIso": "视图：等轴测",
+    "QuickBar.ViewRight": "视图：右",
+    "QuickBar.ViewTop": "视图：上",
+    "QuickBar.ZoomAll": "🔍 显示全部",
+    "Runtime.Align3Completed": "已三点对齐“{0}”（旋转+平移；点 1 精确贴合，测量已清空）",
+    "Runtime.Align3Failed": "三点对齐失败（点位退化），请重新选点",
+    "Runtime.Align3OtherFile": "目标点必须位于另一个文件上",
+    "Runtime.Align3SameSource": "3 个来源点必须位于同一个文件（要移动：{0}）",
+    "Runtime.Align3SourceCollinear": "三点共线，请重新选择不共线的第 3 点",
+    "Runtime.Align3SourceComplete": "已选完 3 个来源点 — 请在目标文件上选择对应点 1/3",
+    "Runtime.Align3SourcePoint": "来源点 {0}/3 — 继续选择“{1}”上的点",
+    "Runtime.Align3TargetCollinear": "目标三点共线，请重新选择不共线的第 3 点",
+    "Runtime.Align3TargetPoint": "目标点 {0}/3 — 继续选择目标文件上的对应点",
+    "Runtime.AlignMoved": "已移动“{0}” Δ({1:F3}, {2:F3}, {3:F3}) mm（测量已清空；可用面距或干涉验证配合）",
+    "Runtime.AlignMoving": "将移动“{0}” — 请在另一个文件上选择目标点",
+    "Runtime.AlignOtherFile": "目标点必须位于另一个文件上",
+    "Runtime.AllVisible": "已全部显示",
+    "Runtime.AngleDetail": "夹角 = {0:F2}°（补角 {1:F2}°）\n方向 1：{2} ({3:F3}, {4:F3}, {5:F3})\n方向 2：{6} ({7:F3}, {8:F3}, {9:F3})\n（两面夹角按法向量计算，互补角请参考补角值）",
+    "Runtime.AngleFirstDirection": "已选择第 1 个方向（{0}）— 选择第 2 个面或边",
+    "Runtime.ArcLength": "弧长",
+    "Runtime.Axis": "{0} 轴",
+    "Runtime.CircleDetail": "直径 = {0}\n半径 = {1}\n{2} = {3}\n圆心 {4}",
+    "Runtime.Circumference": "周长",
+    "Runtime.ComponentName": "组件",
+    "Runtime.ConicalSurface": "圆锥面",
+    "Runtime.CsvEmpty": "没有可导出的测量结果",
+    "Runtime.CsvExported": "已导出 {0} 条测量结果 → {1}",
+    "Runtime.CsvFilter": "CSV 文件 (*.csv)|*.csv",
+    "Runtime.CsvHeader": "标签,类型,明细",
+    "Runtime.CsvTitle": "导出测量结果",
+    "Runtime.CurveDetail": "曲线长度 = {0}\n类型 = {1}",
+    "Runtime.CurveName": "曲线",
+    "Runtime.CustomPlane": "自定义平面",
+    "Runtime.CylinderSurface": "类型 = 圆柱面\n半径 = {0}\n轴向 ({1:F3}, {2:F3}, {3:F3})",
+    "Runtime.DirectionEdge": "边方向",
+    "Runtime.DirectionFace": "面法向量",
+    "Runtime.DirectionMeshFace": "面法向量（网格）",
+    "Runtime.DistanceDetail": "距离 = {0}\nΔX = {1}\nΔY = {2}\nΔZ = {3}\nP1 {4}\nP2 {5}",
+    "Runtime.DistanceFirstPoint": "第 1 点 ({0:F2}, {1:F2}, {2:F2}) — 选择第 2 点",
+    "Runtime.Dragged": "已拖动“{0}” Δ({1:F2}, {2:F2}, {3:F2}) mm（可用干涉检查验证）",
+    "Runtime.Dragging": "正在拖动“{0}”…（松开定位）",
+    "Runtime.DxfParseFailed": "无法解析 DXF 文件",
+    "Runtime.ExtrusionSurface": "拉伸曲面",
+    "Runtime.FaceDetail": "面积 ≈ {0}（网格近似）\n{1}\n三角形数 = {2:N0}",
+    "Runtime.FaceDistanceDetail": "最短距离 ≈ {0}（网格近似）\nΔX = {1}\nΔY = {2}\nΔZ = {3}\n点 1 {4}\n点 2 {5}",
+    "Runtime.FaceDistanceFirstFace": "已选择第 1 个面 — 请选择另一个面",
+    "Runtime.FaceName": "面",
+    "Runtime.FileNotFound": "找不到文件",
+    "Runtime.GapLabel": "间隙 {0}",
+    "Runtime.GeometryProcessed": "几何处理 {0:N0} ms（三角化 {1:N0} ms、边采样 {2:N0} ms{3}）",
+    "Runtime.GizmoApplied": "已对“{0}”应用操作器变换（可用干涉检查验证）",
+    "Runtime.GizmoHint": "操作器：拖动箭头沿轴移动“{0}”，拖动圆环绕轴旋转；松开即可定位",
+    "Runtime.GizmoSelectFile": "操作器：请先在树面板选择要操作的文件",
+    "Runtime.ImportBusy": "正在导入或计算，请稍后再导入",
+    "Runtime.ImportCompleted": "导入完成：成功 {0} 个文件{1}",
+    "Runtime.ImportFailed": "导入失败：{0} — {1}",
+    "Runtime.ImportFailedCount": "、失败 {0} 个文件",
+    "Runtime.ImportFailedTitle": "导入失败",
+    "Runtime.ImportFilter": "CAD 文件 (*.stp;*.step;*.stl;*.dxf)|*.stp;*.step;*.stl;*.dxf|STEP (*.stp;*.step)|*.stp;*.step|STL (*.stl)|*.stl|DXF (*.dxf)|*.dxf|所有文件 (*.*)|*.*",
+    "Runtime.ImportProgress": "导入 {0}：{1}",
+    "Runtime.ImportTitle": "导入 CAD 文件（可多选）",
+    "Runtime.Importing": "正在导入：{0} …",
+    "Runtime.InterferenceChecking": "正在检查干涉（第 {0} 组）：{1} ⟷ {2} …",
+    "Runtime.InterferenceClearDetail": "{0} ⟷ {1} 无相交\n最小间隙 ≈ {2}（网格近似）\n间隙 ≈ 0 表示贴合\n点 1 {3}\n点 2 {4}",
+    "Runtime.InterferenceClearTitle": "🧩 无干涉  间隙 ≈ {0}",
+    "Runtime.InterferenceCompleted": "干涉检查完成：{0} 组配对、{1} 组相交",
+    "Runtime.InterferenceFailed": "干涉检查失败：{0}",
+    "Runtime.InterferenceHitDetail": "零件相交（非贴合）\n相交三角形对 = {0:N0}\n红色线 = 干涉交线（{1:N0} 段）\n（共面贴合不计为干涉）",
+    "Runtime.InterferenceHitTitle": "🧩 发生干涉！{0} ⟷ {1}",
+    "Runtime.InterferenceLabel": "干涉",
+    "Runtime.InterferenceNeedTwo": "干涉检查至少需要 2 个可见文件（当前 {0} 个），请在树面板勾选",
+    "Runtime.Isolated": "只显示“{0}”（树右键 → 全部显示 可恢复）",
+    "Runtime.KindAlign": "对齐",
+    "Runtime.KindAlign3": "三点对齐",
+    "Runtime.KindAngle": "角度",
+    "Runtime.KindCircle": "圆",
+    "Runtime.KindDistance": "距离",
+    "Runtime.KindDrag": "拖动",
+    "Runtime.KindEdge": "边",
+    "Runtime.KindFace": "面",
+    "Runtime.KindFaceDistance": "面距",
+    "Runtime.KindInterference": "干涉",
+    "Runtime.KindNone": "无",
+    "Runtime.KindPoint": "点",
+    "Runtime.KindVolume": "体积",
+    "Runtime.LineDetail": "长度 = {0}\nΔX = {1}  ΔY = {2}  ΔZ = {3}\n起点 {4}\n终点 {5}",
+    "Runtime.MeasureFailed": "测量失败：{0}",
+    "Runtime.MeasurementStartCancelled": "已取消当前测量起点（再次按 Esc 退出测量模式）",
+    "Runtime.MeasurementsCleared": "已清除全部测量",
+    "Runtime.MeshMeasurementLimited": "此模型无 B-rep（STL/网格），仅支持点、距离、角度和面距测量",
+    "Runtime.MeshName": "网格",
+    "Runtime.MeshNameNumbered": "网格 {0}",
+    "Runtime.MeshSurface": "类型 = 网格（无 B-rep）",
+    "Runtime.ModeAlign": "两点对齐：先点要移动零件上的点，再点目标点（仅平移，测量将清空）",
+    "Runtime.ModeAlign3": "三点对齐：先在要移动的文件中选 3 个特征点，再在目标文件中选 3 个对应点（旋转+平移）",
+    "Runtime.ModeAngle": "角度测量：选择第 1 个面（或直线边附近）",
+    "Runtime.ModeBrowse": "浏览模式（右键旋转、滚轮缩放、中键或 Shift+左键拖动平移）",
+    "Runtime.ModeCircle": "圆测量：点击圆孔内壁或圆边附近",
+    "Runtime.ModeDistance": "距离测量：选择第 1 点",
+    "Runtime.ModeDrag": "拖动模式：按住左键沿屏幕平面移动零件，松开定位；需改变深度时请先旋转视角",
+    "Runtime.ModeEdge": "边测量：点击要测量的边附近",
+    "Runtime.ModeFace": "面测量：点击要测量的面",
+    "Runtime.ModeFaceDistance": "面距测量：选择第 1 个面",
+    "Runtime.ModePoint": "点测量：点击模型表面（自动吸附邻近顶点）",
+    "Runtime.NoBrep": " · 无 B-rep",
+    "Runtime.NoCircularEdge": "此面没有圆形边（请点击圆孔内壁或圆边附近）",
+    "Runtime.NoGeometry": "文件中没有可显示的几何",
+    "Runtime.NoMeasurableEdge": "此面没有可测量的边",
+    "Runtime.NoSurfaceHit": "未命中模型表面",
+    "Runtime.NodeStats": "{0} 实体 · {1} 面 · {2:N0} △",
+    "Runtime.NurbsSurface": "NURBS 曲面",
+    "Runtime.Orthographic": "正交投影（平行投影，适合尺寸确认）",
+    "Runtime.OutlineSize": "\n外形 {0}",
+    "Runtime.ParsingStep": "解析 STEP（大文件可能需要数分钟）…",
+    "Runtime.ParsingStl": "解析 STL（三角形直读）…",
+    "Runtime.Perspective": "透视投影",
+    "Runtime.PlaneSurface": "类型 = 平面\n法向量 ({0:F3}, {1:F3}, {2:F3})",
+    "Runtime.Ready": "就绪 — 导入 STP/STEP/STL/DXF（也可拖放）。右键旋转、滚轮缩放、中键或 Shift+左键平移",
+    "Runtime.Removed": "已移除：{0}",
+    "Runtime.RetriedFaces": "、重试补回 {0} 面",
+    "Runtime.Reversed": "（反向）",
+    "Runtime.RevolutionSurface": "旋转曲面",
+    "Runtime.RootNotFound": "找不到此零件所属文件",
+    "Runtime.RotateSelectFile": "请先在树面板选择要旋转的文件",
+    "Runtime.Rotated": "已将“{0}”绕 {1} 轴旋转 +90°（再次点击可继续旋转）",
+    "Runtime.SameFace": "两次选中了同一个面，请选择另一个面",
+    "Runtime.ScreenshotFilter": "PNG 图片 (*.png)|*.png",
+    "Runtime.ScreenshotSaved": "已保存截图 → {0}",
+    "Runtime.ScreenshotTitle": "保存视图截图",
+    "Runtime.SectionCancelled": "已取消三点剖面定义",
+    "Runtime.SectionClosed": "剖面已关闭",
+    "Runtime.SectionCollinear": "三点剖面：三点共线，请选择不共线的第 3 点",
+    "Runtime.SectionDefined": "三点剖面：平面已定义（法向 {0:F2}, {1:F2}, {2:F2}）— 用位置滑块扫描剖面",
+    "Runtime.SectionDegenerate": "三点剖面：三点退化（共线），请重新选择",
+    "Runtime.SectionNoHit": "三点剖面：未命中模型表面（已选 {0}/3 点，Esc 取消）",
+    "Runtime.SectionPickPrompt": "三点剖面：请在模型上选择 3 个点定义剖切平面（Esc 取消）",
+    "Runtime.SectionPicked": "三点剖面：已选 {0}/3 点",
+    "Runtime.SectionStatus": "剖面：{0} {1:F0}%{2}",
+    "Runtime.ShellName": "壳体",
+    "Runtime.SolidName": "实体",
+    "Runtime.SphericalSurface": "球面",
+    "Runtime.StepExportEmpty": "没有可导出的 B-rep 几何（STEP 仅包含 Solid/Shell；请勾选要导出的 STEP 文件）",
+    "Runtime.StepExportFailed": "STEP 导出失败：{0}",
+    "Runtime.StepExportFilter": "STEP 文件 (*.stp)|*.stp|STEP 文件 (*.step)|*.step",
+    "Runtime.StepExportTitle": "将当前场景导出为 STEP（零件处于当前对齐位置）",
+    "Runtime.StepExported": "已导出 STEP（{0} 个实体，当前位置）→ {1}",
+    "Runtime.StepParseFailed": "CADability 无法解析此 STEP 文件",
+    "Runtime.StepParsed": "STEP 解析 {0:N0} ms",
+    "Runtime.StlExportEmpty": "没有可导出的网格（请勾选至少一个含实体网格的文件）",
+    "Runtime.StlExportFailed": "STL 导出失败：{0}",
+    "Runtime.StlExportFilter": "STL 文件 (*.stl)|*.stl",
+    "Runtime.StlExportMergedTitle": "导出 STL（合并为单个文件）",
+    "Runtime.StlExportPerFileTitle": "导出 STL（每个文件分别导出，以此作为基础文件名）",
+    "Runtime.StlExportedMany": "已导出 {0} 个 STL（共 {1:N0} 个三角形）→ {2}",
+    "Runtime.StlExportedOne": "已导出 STL（{0:N0} 个三角形）→ {1}",
+    "Runtime.StlExporting": "正在导出 STL…",
+    "Runtime.StlNoTriangles": "STL 文件中没有三角形",
+    "Runtime.StlParsed": "STL 解析 {0:N0} ms（{1} 个网格）",
+    "Runtime.StlRetriangulating": "正在重新三角化并导出 STL…（大型装配需要时间）",
+    "Runtime.SurfaceType": "类型 = {0}",
+    "Runtime.ToroidalSurface": "环面",
+    "Runtime.Triangulating": "并行三角化 {0} 个零件…",
+    "Runtime.UnitInch": "显示单位：inch",
+    "Runtime.UnitMillimeter": "显示单位：mm",
+    "Runtime.UnsupportedFormat": "不支持的格式（支持 .stp / .step / .stl / .dxf；CADability 无 IGES reader）",
+    "Runtime.View": "视图：{0}",
+    "Runtime.ViewBack": "后",
+    "Runtime.ViewBottom": "下",
+    "Runtime.ViewFront": "前",
+    "Runtime.ViewIso": "等角",
+    "Runtime.ViewLeft": "左",
+    "Runtime.ViewRight": "右",
+    "Runtime.ViewTop": "上",
+    "Runtime.VisibilityInverted": "已反转显示",
+    "Runtime.VolumeDetail": "体积 ≈ {0}（网格近似）\n质心 {1}\n外形（AABB）{2} × {3} × {4} {5}",
+    "Runtime.VolumeNoMesh": "“{0}”没有可计算的面网格（线框无体积）",
+    "Runtime.VolumeOpenMesh": "“{0}”不是封闭网格，无法可靠计算体积",
+    "Ui.About.Changelog": "📋  版本纪录",
+    "Ui.About.Close": "关闭",
+    "Ui.About.Description": "STP / STEP 3D 查看器。免开重量级 CAD，快速打开文件、测量、对齐插合、干涉检查、剖面、导出。",
+    "Ui.About.Developer": "👤  开发者",
+    "Ui.About.Email": "邮箱",
+    "Ui.About.Name": "姓名",
+    "Ui.About.Release010.Change1": "• STEP／STL／DXF 导入与装配树、点／距离／边／面／圆／角度／面距测量、两点与三点对齐、干涉检查、剖面、mm ⇄ inch、CSV 与截图导出。",
+    "Ui.About.Release010.Title": "首次发布",
+    "Ui.About.Release020.Change1": "• 添加拖曳模式：左键按住零件直接拖到想要的位置，放开就定位。",
+    "Ui.About.Release020.Change2": "• 0.2.1 修正拖曳过的零件再点击会当掉的问题。",
+    "Ui.About.Release020.Title": "拖曳模式",
+    "Ui.About.Release030.Change1": "• 添加操作器：选取文件后出现 XYZ 三色箭头与旋转环，箭头沿轴精确移动、旋转环绕轴转任意角度。",
+    "Ui.About.Release030.Title": "三轴操作器",
+    "Ui.About.Release031.Change1": "• 三轴操作器改成永远浮在画面最上层，不会被零件挡住，任何角度都抓得到。",
+    "Ui.About.Release031.Title": "操作器永远可见",
+    "Ui.About.Release032.Change1": "• 修正大型组件（数万个面）进入测量模式后，转动视角严重卡顿的问题 — 现在测量跟浏览一样顺。",
+    "Ui.About.Release032.Title": "大组件测量不再卡",
+    "Ui.About.Release040.Change1": "• 大文件拉剖面滑杆不再卡住画面（改到背景计算）。",
+    "Ui.About.Release040.Change2": "• 拖曳／操作器放开零件后的定位计算大幅加速。",
+    "Ui.About.Release040.Change3": "• 程序遇到错误会提示消息并继续运作，不再整个闪退。",
+    "Ui.About.Release040.Title": "更快、更稳",
+    "Ui.About.Release050.Change1": "• 量距离时点到圆孔边缘会自动吸到圆心 — 量两孔中心距（pitch）超方便。",
+    "Ui.About.Release050.Change2": "• 测量快速键：P 点、D 距离、E 边、F 面、C 圆、A 角度、M 面距；Esc 取消。",
+    "Ui.About.Release050.Change3": "• 树状面板可搜索零件名称；右键可「只显示此节点」隔离观察，也可以量体积与质心。",
+    "Ui.About.Release050.Change4": "• 添加标准视图（等角／前／上／右）与正交投影，量尺寸不受透视变形。",
+    "Ui.About.Release050.Change5": "• 剖面添加「3点」模式：在模型上点 3 个点，就能沿任意斜面剖开。",
+    "Ui.About.Release050.Change6": "• 添加导出 STEP：把对齐好的零件位置存成新 STEP 文件，交接给正式 CAD。",
+    "Ui.About.Release050.Change7": "• 会记住窗口大小、单位设置与最近打开的 10 个文件。",
+    "Ui.About.Release050.Title": "测量、视图、树状面板大升级",
+    "Ui.About.Release060.Change1": "• 添加导出 STL：把画面上的零件（含对齐、旋转后的位置）存成 STL 网格文件，可拿去 3D 打印或给其他软件用。",
+    "Ui.About.Release060.Change2": "• 导出前会先跳出设置窗口：全部合并成一个文件或每个文件各存一个、Binary 或文本格式、mm 或 inch、网格精细度 — 确认后才导出。",
+    "Ui.About.Release060.Change3": "• 设置窗口会即时显示三角形数量与预估文件大小。",
+    "Ui.About.Release060.Title": "导出 STL",
+    "Ui.About.Release070.Change1": "• 上方添加菜单栏，全部功能依「文件／视图／测量／变换／工具」分类，不用再在一长排按钮里找。",
+    "Ui.About.Release070.Change2": "• 原本的工具栏变成「快捷栏」：只放常用按钮。想放哪些自己决定 — 到「快捷栏 → 自定义按钮」勾选，下次打开会记住。",
+    "Ui.About.Release070.Change3": "• 剖面的轴向／位置控制列改成只在打开剖面时出现，平常不占空间。",
+    "Ui.About.Release070.Change4": "• 添加「关于」窗口（就是这个画面），可以看版本纪录。",
+    "Ui.About.Release070.Title": "界面大改版 — 菜单栏＋可自定义快捷栏",
+    "Ui.About.Release071.Change1": "• 打开大型 STL 网格文件（数十 MB、上百万三角形）现在几乎瞬间完成，不用再等好几分钟。",
+    "Ui.About.Release071.Change2": "• 例如一个 75 MB、150 万个三角形的 STL，以前要等到天荒地老，现在不到 1 秒就显示出来。",
+    "Ui.About.Release071.Title": "大型 STL 秒开",
+    "Ui.About.Technology": ".NET 8 · WPF · C#；CADability（STEP / B-rep 几何内核）；HelixToolkit（3D 显示与相机）",
+    "Ui.About.TechnologyTitle": "🔧  技术栈",
+    "Ui.About.Title": "关于 STPViewer",
+    "Ui.Language": "语言",
+    "Ui.Main.3AxisGizmo": "⊹ 三轴操作器",
+    "Ui.Main.3AxisGizmoUseXYZArrows": "三轴操作器：对树面板选取的文件显示 XYZ 箭头（沿轴移动）与旋转环（绕轴转任意角度），每次放开即定位",
+    "Ui.Main.3Point": "🎯 三点",
+    "Ui.Main.3Points": "3点",
+    "Ui.Main.Align": "🎯 对齐",
+    "Ui.Main.Angle": "∠ 角度",
+    "Ui.Main.AngleBetweenFacesStraightEdgesShortcut": "两面/两边夹角（点两个面或靠近直线边）— 快速键 A",
+    "Ui.Main.AngleBetweenTwoFacesStraightEdges": "两面/两边夹角（点两个面或靠近直线边）",
+    "Ui.Main.ApplicationInformationReleaseHistory": "程序信息与版本纪录",
+    "Ui.Main.AreaSurfaceTypeNormalVector": "面积 + 曲面类型/法矢量",
+    "Ui.Main.AreaSurfaceTypeNormalVectorShortcut": "面积 + 曲面类型/法矢量 — 快速键 F",
+    "Ui.Main.Capture": "📷 截图",
+    "Ui.Main.CenterRadiusDiameterCircumference": "圆心/半径/直径/周长",
+    "Ui.Main.CenterRadiusDiameterCircumferenceShortcutC": "圆心/半径/直径/周长 — 快速键 C",
+    "Ui.Main.CheckButtonsShowQuickBarSaved": "勾选要显示在快捷栏的常用按钮（随设置保存）",
+    "Ui.Main.CheckVisibleModelPairsIntersectionsReport": "2 个以上可见文件两两检查是否相交；无相交时回报最小间隙",
+    "Ui.Main.ChooseScopeFormatUnitsMeshQuality": "先设置范围/格式/单位/精度，确认再导出",
+    "Ui.Main.Circle": "⭕ 圆",
+    "Ui.Main.Clear": "🧹 清除",
+    "Ui.Main.ClearAllMeasurements": "🧹 清除全部测量",
+    "Ui.Main.ClearAllMeasurementsMarkersEscCancels": "清除全部测量与标记（Esc = 取消进行中测量/退出模式）",
+    "Ui.Main.ClickChangeColorIncludingChildNodes": "点击换色（含子节点）",
+    "Ui.Main.Close": "✕ 关闭",
+    "Ui.Main.CloseSectionView": "关闭剖面查看",
+    "Ui.Main.CustomizeButtons": "自定义按钮",
+    "Ui.Main.DeleteThisMeasurement": "删除此笔测量",
+    "Ui.Main.DisplayInchesMm": "单位显示 inch（mm ⇄ in）",
+    "Ui.Main.Distance": "📏 距离",
+    "Ui.Main.DistanceXYZCircleCenterSnappingHole": "两点距离 + ΔXYZ（点到圆边会吸圆心 → 可量孔对孔 pitch）— 快速键 D",
+    "Ui.Main.DistanceXYZCircularEdgesSnapCenters": "两点距离 + ΔXYZ（点到圆边会吸圆心 → 可量孔对孔 pitch）",
+    "Ui.Main.Drag": "🖐 拖曳",
+    "Ui.Main.DragMode": "🖐 拖曳模式",
+    "Ui.Main.DragModeHoldLeftMouseButton": "拖曳模式：左键按住零件沿屏幕平面拖动，放开定位（深度方向先转视角再拖）",
+    "Ui.Main.DragResizePanel": "拖曳调整面板宽度",
+    "Ui.Main.Edge": "📐 边",
+    "Ui.Main.EdgeLength": "📐 边长",
+    "Ui.Main.Edges": "边",
+    "Ui.Main.EscCancelsCurrentMeasurementExitsMode": "Esc = 取消进行中测量/退出模式",
+    "Ui.Main.ExistingMeasurementsUpdateImmediatelyValuesStored": "既有测量即时换算；内部一律存 mm",
+    "Ui.Main.ExportMeasurementResultsCSV": "测量结果导出 CSV",
+    "Ui.Main.ExportMeasurementsCSV": "💾 导出测量 CSV…",
+    "Ui.Main.ExportSTEP": "📤 导出 STEP…",
+    "Ui.Main.ExportSTL": "📐 导出 STL…",
+    "Ui.Main.ExportStepTooltip": "把可见文件（当前对齐位置）导出成新 STEP 文件；不动源文件",
+    "Ui.Main.Face": "⬛ 面",
+    "Ui.Main.FaceDistance": "⇔ 面距",
+    "Ui.Main.FileF": "文件(_F)",
+    "Ui.Main.FilterAssemblyTreeByNameDoes": "输入名称过滤装配树（只影响树面板显示，不影响 3D 可见性；清空 = 全显）",
+    "Ui.Main.Fit": "🔍 全览",
+    "Ui.Main.FitAllModelsView": "缩放至全部模型",
+    "Ui.Main.Flip": "反向",
+    "Ui.Main.Front": "前",
+    "Ui.Main.FrontView": "前视图",
+    "Ui.Main.FrontViewLookAlongYZ": "前视图（-Y 方向看，Z 向上）",
+    "Ui.Main.Gizmo": "⊹ 操作器",
+    "Ui.Main.HelpH": "说明(_H)",
+    "Ui.Main.HoldLeftMouseButtonMovePart": "左键按住零件沿屏幕平面拖动，放开定位",
+    "Ui.Main.IAboutSTPViewer": "ℹ 关于 STPViewer…",
+    "Ui.Main.ImportSTPSTEPSTLDXFFiles": "导入 STP/STEP/STL/DXF（可多选，也可直接拖放到窗口）",
+    "Ui.Main.Interference": "🧩 干涉",
+    "Ui.Main.InterferenceCheck": "🧩 干涉检查",
+    "Ui.Main.InterferenceCheckTestVisibleModelPairs": "干涉检查：2 个以上可见文件两两检查是否相交（match 判定）；无相交时回报最小间隙",
+    "Ui.Main.InvertVisibility": "🔄 反转显示",
+    "Ui.Main.Iso": "等角",
+    "Ui.Main.IsometricView": "等角视图",
+    "Ui.Main.LookAlongXZUp": "+X 方向看，Z 向上",
+    "Ui.Main.LookAlongYZUp": "-Y 方向看，Z 向上",
+    "Ui.Main.LookDownFromZ": "+Z 往下看",
+    "Ui.Main.MeasureM": "测量(_M)",
+    "Ui.Main.MeasurePointCoordinatesSnapsVerticesCircle": "测量点坐标（吸附顶点/圆心）",
+    "Ui.Main.MeasureStraightCurvedCircularEdgeLengths": "边长（直线/曲线/圆弧）",
+    "Ui.Main.MeasureVolumeCentroid": "⚖ 量体积 / 质心",
+    "Ui.Main.Measurements": "测量结果",
+    "Ui.Main.MenuImport": "📂 导入…",
+    "Ui.Main.ModelsAssemblyTree": "模型 / 装配树",
+    "Ui.Main.Ortho": "正交",
+    "Ui.Main.OrthographicProjection": "正交投影",
+    "Ui.Main.OrthographicProjectionAvoidsPerspectiveDistortionClick": "正交投影（平行投影，量尺寸不受透视变形；再按切回透视）",
+    "Ui.Main.ParallelProjectionAvoidsPerspectiveDistortionUncheck": "平行投影，量尺寸不受透视变形；取消勾选切回透视",
+    "Ui.Main.PickPointPartMoveThenPick": "先点要移动零件上的点，再点目标点",
+    "Ui.Main.PickThreePointsMovingModelThen": "先在要移动的文件点 3 个特征点，再到目标文件点 3 个对应点（顺序对应）",
+    "Ui.Main.Point": "📍 点",
+    "Ui.Main.PointCoordinates": "📍 点坐标",
+    "Ui.Main.PointCoordinatesVertexCircleCenterSnapping": "测量点坐标（吸附顶点/圆心）— 快速键 P",
+    "Ui.Main.QuickBarQ": "快捷栏(_Q)",
+    "Ui.Main.RecentFiles": "最近文件",
+    "Ui.Main.RecentlyOpenedFiles": "最近打开的文件",
+    "Ui.Main.RemoveThisFile": "移除此文件",
+    "Ui.Main.RestoreDefaultButtons": "恢复缺省按钮",
+    "Ui.Main.Right": "右",
+    "Ui.Main.RightView": "右视图",
+    "Ui.Main.RightViewLookAlongXZ": "右视图（+X 方向看，Z 向上）",
+    "Ui.Main.Rotate90AroundX": "↻ 绕 X 轴 +90°",
+    "Ui.Main.Rotate90AroundY": "↻ 绕 Y 轴 +90°",
+    "Ui.Main.Rotate90AroundZ": "↻ 绕 Z 轴 +90°",
+    "Ui.Main.RotateModelSelectedTree90Around": "选取的文件绕 X 轴 +90°（先在树面板点击文件）",
+    "Ui.Main.RotateModelSelectedTreeAroundIts": "对树面板选取的文件，绕其中心旋转（先在树面板点击文件）",
+    "Ui.Main.RotateSelectedModel90AroundY": "选取的文件绕 Y 轴 +90°",
+    "Ui.Main.RotateSelectedModel90AroundZ": "选取的文件绕 Z 轴 +90°",
+    "Ui.Main.SavePNGScreenshot3DView2": "3D 视图截图存 PNG（2x 分辨率）",
+    "Ui.Main.SaveViewPNG": "📷 视图截图 PNG…",
+    "Ui.Main.SectionAxis3PointsDefineAn": "剖切轴向（3点 = 在模型上点 3 点定义任意平面）",
+    "Ui.Main.SectionLabel": "✂ 剖面：",
+    "Ui.Main.SectionPosition0100EnterValue": "剖面位置 %（0–100，可直接输入，离开字段生效）",
+    "Ui.Main.SectionPositionAlongNormal": "剖面位置（沿法向 %）",
+    "Ui.Main.SectionView": "✂ 剖面查看",
+    "Ui.Main.ShortestDistanceBetweenFacesMeshApproximation": "面到面最短距离（网格近似）",
+    "Ui.Main.ShortestFaceDistanceMeshApproximationShortcut": "面到面最短距离（网格近似）— 快速键 M",
+    "Ui.Main.ShowAll": "☀ 全部显示",
+    "Ui.Main.ShowHideIncludingChildNodes": "显示 / 隐藏（含子节点）",
+    "Ui.Main.ShowOnlyThisNode": "👁 只显示此节点",
+    "Ui.Main.ShowOutlineEdgesManyEdgesCan": "显示轮廓边线（边线量大时转动视角会变慢）",
+    "Ui.Main.ShowSectionControlsAxisPositionDirection": "打开后下方出现剖面参数表（轴向/位置/反向）",
+    "Ui.Main.ShowXYZArrowsRotationRingsSelected": "对树面板选取的文件显示 XYZ 箭头与旋转环，每次放开即定位",
+    "Ui.Main.StraightCurvedCircularEdgeLengthShortcut": "边长（直线/曲线/圆弧）— 快速键 E",
+    "Ui.Main.SwitchDisplayUnitsBetweenMmInches": "切换显示单位 mm ⇄ inch（既有测量即时换算）",
+    "Ui.Main.SwitchRetainedSide": "切换保留侧",
+    "Ui.Main.ThreePointAlignmentPickThreePoints": "三点对齐（旋转+平移）：先在要移动的文件点 3 个特征点，再到目标文件点 3 个对应点（顺序对应）",
+    "Ui.Main.ThreePointAlignmentRotateTranslate": "🎯 三点对齐（旋转+平移）",
+    "Ui.Main.ToggleSectionViewItsControls": "打开/关闭剖面查看（打开后下方出现参数表）",
+    "Ui.Main.ToolbarExportStepTooltip": "把可见文件（当前对齐位置）导出成新 STEP 文件 — 对齐插合结果可交接 CAD；不动源文件",
+    "Ui.Main.ToolbarExportStlTooltip": "把可见文件（当前位置）导出成 STL 网格文件 — 先设置范围/格式/单位/精度，确认再导出",
+    "Ui.Main.ToolbarImport": "📂 导入",
+    "Ui.Main.ToolbarSection": "✂ 剖面",
+    "Ui.Main.ToolsL": "工具(_L)",
+    "Ui.Main.Top": "上",
+    "Ui.Main.TopView": "上视图",
+    "Ui.Main.TopViewLookDownFromZ": "上视图（+Z 往下看）",
+    "Ui.Main.TransformT": "变换(_T)",
+    "Ui.Main.TwoPointAlignmentPickPointMoving": "两点对齐（平移零件）：先点要移动零件上的点，再点目标点",
+    "Ui.Main.TwoPointAlignmentTranslate": "🎯 两点对齐（平移）",
+    "Ui.Main.TwoPointDistance": "📏 两点距离",
+    "Ui.Main.ViewV": "视图(_V)",
+    "Ui.Main.WindowTitle": "STPViewer — STP/STEP 3D 查看器",
+    "Ui.Main.ZoomFit": "🔍 缩放至全部",
+    "Ui.Main.ZoomThisNode": "缩放至此节点",
+    "Ui.StlExport.Cancel": "取消",
+    "Ui.StlExport.CustomScaleTooltip": "坐标乘上此系数（例：0.001 = mm→m）",
+    "Ui.StlExport.EstimatedSize": "预估 {0}",
+    "Ui.StlExport.EstimatedSizeFine": "以当前网格预估 {0}（实际依重新三角化结果）",
+    "Ui.StlExport.Export": "导出…",
+    "Ui.StlExport.Format": "格式",
+    "Ui.StlExport.FormatAscii": "ASCII（文本可读，文件约 4 倍大）",
+    "Ui.StlExport.FormatBinary": "Binary（建议，文件小）",
+    "Ui.StlExport.MeshQuality": "网格精度",
+    "Ui.StlExport.QualityCurrent": "当前显示网格（快，与画面一致）",
+    "Ui.StlExport.QualityFine": "精细 — 重新三角化，曲面更平滑（慢、文件大）",
+    "Ui.StlExport.QualityTooltip": "精细会由 B-rep 重新三角化（仅 STEP 来源；STL/DXF 维持现有网格），大组件需要时间",
+    "Ui.StlExport.Scope": "导出范围",
+    "Ui.StlExport.ScopeMerge": "全部可见文件 → 合并成单一 STL",
+    "Ui.StlExport.ScopePerFile": "每个可见文件 → 各一个 STL",
+    "Ui.StlExport.ScopeTooltip": "STL 无装配结构；合并 = 所有可见零件进同一个文件",
+    "Ui.StlExport.Summary": "{0} 个可见文件 · {1} 三角形 · {2}",
+    "Ui.StlExport.Title": "导出 STL — 参数设置",
+    "Ui.StlExport.UnitCustom": "自定义缩放系数…",
+    "Ui.StlExport.UnitInch": "inch（坐标 ÷ 25.4）",
+    "Ui.StlExport.UnitMillimeter": "mm（1:1，缺省）",
+    "Ui.StlExport.UnitScale": "单位缩放",
+    "Ui.StlExport.UnitTooltip": "STL 文件本身无单位；内部几何为 mm，选 inch 会把坐标 ÷25.4"
+  }
+}
diff --git a/src/STPViewer/i18n/zh_tw.json b/src/STPViewer/i18n/zh_tw.json
new file mode 100644
index 0000000..893b3ba
--- /dev/null
+++ b/src/STPViewer/i18n/zh_tw.json
@@ -0,0 +1,417 @@
+{
+  "key": "繁體中文",
+  "data": {
+    "App.ErrorTitle": "STPViewer 錯誤",
+    "App.NoRecentFiles": "（沒有最近開啟的檔案）",
+    "App.UnexpectedError": "發生未預期的錯誤，操作已中止（程式將嘗試繼續運作）。\n\n{0}\n\n詳細記錄：{1}",
+    "App.WindowTitle": "STPViewer V{0} — STP/STEP 3D 檢視器",
+    "QuickBar.Align": "🎯 兩點對齊",
+    "QuickBar.Align3": "🎯 三點對齊",
+    "QuickBar.Angle": "∠ 角度",
+    "QuickBar.Circle": "⭕ 圓",
+    "QuickBar.Clear": "🧹 清除量測",
+    "QuickBar.Distance": "📏 距離",
+    "QuickBar.Drag": "🖐 拖曳",
+    "QuickBar.Edge": "📐 邊",
+    "QuickBar.ExportCsv": "💾 匯出 CSV",
+    "QuickBar.ExportStep": "📤 匯出 STEP",
+    "QuickBar.ExportStl": "📐 匯出 STL",
+    "QuickBar.Face": "⬛ 面",
+    "QuickBar.FaceDistance": "⇔ 面距",
+    "QuickBar.Gizmo": "⊹ 操作器",
+    "QuickBar.Import": "📂 匯入",
+    "QuickBar.Interference": "🧩 干涉",
+    "QuickBar.Language": "語言",
+    "QuickBar.Ortho": "正交投影",
+    "QuickBar.Point": "📍 點",
+    "QuickBar.Recent": "▾ 最近檔案",
+    "QuickBar.RotateX": "旋轉 ↻X",
+    "QuickBar.RotateY": "旋轉 ↻Y",
+    "QuickBar.RotateZ": "旋轉 ↻Z",
+    "QuickBar.Screenshot": "📷 截圖",
+    "QuickBar.Section": "✂ 剖面",
+    "QuickBar.Unit": "mm ⇄ in",
+    "QuickBar.ViewFront": "視圖：前",
+    "QuickBar.ViewIso": "視圖：等角",
+    "QuickBar.ViewRight": "視圖：右",
+    "QuickBar.ViewTop": "視圖：上",
+    "QuickBar.ZoomAll": "🔍 全覽",
+    "Runtime.Align3Completed": "已三點對齊「{0}」（旋轉+平移；點1精確貼合，量測已清空，可用 🧩干涉 驗證）",
+    "Runtime.Align3Failed": "三點對齊失敗（點位退化），請重新選點",
+    "Runtime.Align3OtherFile": "目標點要點在另一個檔案上",
+    "Runtime.Align3SameSource": "來源 3 點要同一個檔案（要移動：{0}）",
+    "Runtime.Align3SourceCollinear": "三點共線，請改選不共線的第 3 點",
+    "Runtime.Align3SourceComplete": "來源 3 點完成 — 換點「目標檔案」上的對應點 1/3",
+    "Runtime.Align3SourcePoint": "來源點 {0}/3 — 繼續點「{1}」上的點",
+    "Runtime.Align3TargetCollinear": "目標三點共線，請改選不共線的第 3 點",
+    "Runtime.Align3TargetPoint": "目標點 {0}/3 — 繼續點目標檔案上的對應點",
+    "Runtime.AlignMoved": "已移動「{0}」 Δ({1:F3}, {2:F3}, {3:F3}) mm（量測已清空；可用 ⇔面距 / 🧩干涉 驗證配合）",
+    "Runtime.AlignMoving": "將移動「{0}」— 點選目標點（另一個檔案上）",
+    "Runtime.AlignOtherFile": "目標點要點在另一個檔案上（兩點同屬一個檔案無法對齊）",
+    "Runtime.AllVisible": "已全部顯示",
+    "Runtime.AngleDetail": "夾角 = {0:F2}°（補角 {1:F2}°）\n方向 1：{2} ({3:F3}, {4:F3}, {5:F3})\n方向 2：{6} ({7:F3}, {8:F3}, {9:F3})\n（兩面夾角以法向量計，互補角請參考補角值）",
+    "Runtime.AngleFirstDirection": "已選第 1 個方向（{0}）— 點選第 2 個面或邊",
+    "Runtime.ArcLength": "弧長",
+    "Runtime.Axis": "{0} 軸",
+    "Runtime.CircleDetail": "直徑 = {0}\n半徑 = {1}\n{2} = {3}\n圓心 {4}",
+    "Runtime.Circumference": "周長",
+    "Runtime.ComponentName": "組件",
+    "Runtime.ConicalSurface": "圓錐面",
+    "Runtime.CsvEmpty": "沒有量測結果可匯出",
+    "Runtime.CsvExported": "已匯出 {0} 筆量測 → {1}",
+    "Runtime.CsvFilter": "CSV 檔案 (*.csv)|*.csv",
+    "Runtime.CsvHeader": "標籤,類型,明細",
+    "Runtime.CsvTitle": "匯出量測結果",
+    "Runtime.CurveDetail": "曲線長 = {0}\n類型 = {1}",
+    "Runtime.CurveName": "曲線",
+    "Runtime.CustomPlane": "自訂平面",
+    "Runtime.CylinderSurface": "類型 = 圓柱面\n半徑 = {0}\n軸向 ({1:F3}, {2:F3}, {3:F3})",
+    "Runtime.DirectionEdge": "邊方向",
+    "Runtime.DirectionFace": "面法向量",
+    "Runtime.DirectionMeshFace": "面法向量（網格）",
+    "Runtime.DistanceDetail": "距離 = {0}\nΔX = {1}\nΔY = {2}\nΔZ = {3}\nP1 {4}\nP2 {5}",
+    "Runtime.DistanceFirstPoint": "第 1 點 ({0:F2}, {1:F2}, {2:F2}) — 點選第 2 點",
+    "Runtime.Dragged": "已拖曳「{0}」 Δ({1:F2}, {2:F2}, {3:F2}) mm（可用 🧩干涉 驗證）",
+    "Runtime.Dragging": "拖曳「{0}」中…（放開定位）",
+    "Runtime.DxfParseFailed": "無法解析 DXF 檔",
+    "Runtime.ExtrusionSurface": "拉伸曲面",
+    "Runtime.FaceDetail": "面積 ≈ {0}（網格近似）\n{1}\n三角形數 = {2:N0}",
+    "Runtime.FaceDistanceDetail": "最短距離 ≈ {0}（網格近似）\nΔX = {1}\nΔY = {2}\nΔZ = {3}\n點 1 {4}\n點 2 {5}",
+    "Runtime.FaceDistanceFirstFace": "已選第 1 個面 — 點選另一個面",
+    "Runtime.FaceName": "面",
+    "Runtime.FileNotFound": "找不到檔案",
+    "Runtime.GapLabel": "gap {0}",
+    "Runtime.GeometryProcessed": "幾何處理 {0:N0} ms（三角化 {1:N0} ms、邊取樣 {2:N0} ms{3}）",
+    "Runtime.GizmoApplied": "已套用操作器變換「{0}」（可用 🧩干涉 驗證）",
+    "Runtime.GizmoHint": "操作器：拖箭頭沿軸移動「{0}」、拖環繞軸旋轉；放開即定位",
+    "Runtime.GizmoSelectFile": "操作器：請先在樹面板點選要操作的檔案",
+    "Runtime.ImportBusy": "忙碌中（匯入或運算進行中），請稍候再匯入",
+    "Runtime.ImportCompleted": "匯入完成：成功 {0} 檔{1}",
+    "Runtime.ImportFailed": "匯入失敗：{0} — {1}",
+    "Runtime.ImportFailedCount": "、失敗 {0} 檔",
+    "Runtime.ImportFailedTitle": "匯入失敗",
+    "Runtime.ImportFilter": "CAD 檔案 (*.stp;*.step;*.stl;*.dxf)|*.stp;*.step;*.stl;*.dxf|STEP (*.stp;*.step)|*.stp;*.step|STL (*.stl)|*.stl|DXF (*.dxf)|*.dxf|所有檔案 (*.*)|*.*",
+    "Runtime.ImportProgress": "匯入 {0}：{1}",
+    "Runtime.ImportTitle": "匯入 CAD 檔案（可複選）",
+    "Runtime.Importing": "匯入中：{0} …",
+    "Runtime.InterferenceChecking": "干涉檢查中（第 {0} 組）：{1} ⟷ {2} …",
+    "Runtime.InterferenceClearDetail": "{0} ⟷ {1} 無相交\n最小間隙 ≈ {2}（網格近似）\ngap ≈ 0 即為貼合（match）\n點 1 {3}\n點 2 {4}",
+    "Runtime.InterferenceClearTitle": "🧩 無干涉  gap ≈ {0}",
+    "Runtime.InterferenceCompleted": "干涉檢查完成：{0} 組配對、{1} 組相交",
+    "Runtime.InterferenceFailed": "干涉檢查失敗：{0}",
+    "Runtime.InterferenceHitDetail": "兩零件相交（不 match）\n相交三角形對 = {0:N0}\n紅色線 = 干涉交線（{1:N0} 段）\n（共面貼合不會被算為干涉）",
+    "Runtime.InterferenceHitTitle": "🧩 干涉！{0} ⟷ {1}",
+    "Runtime.InterferenceLabel": "干涉",
+    "Runtime.InterferenceNeedTwo": "干涉檢查需要至少 2 個可見檔案（目前 {0} 個）— 用樹面板勾選",
+    "Runtime.Isolated": "只顯示「{0}」（樹右鍵 → 全部顯示 復原）",
+    "Runtime.KindAlign": "對齊",
+    "Runtime.KindAlign3": "三點對齊",
+    "Runtime.KindAngle": "角度",
+    "Runtime.KindCircle": "圓",
+    "Runtime.KindDistance": "距離",
+    "Runtime.KindDrag": "拖曳",
+    "Runtime.KindEdge": "邊",
+    "Runtime.KindFace": "面",
+    "Runtime.KindFaceDistance": "面距",
+    "Runtime.KindInterference": "干涉",
+    "Runtime.KindNone": "無",
+    "Runtime.KindPoint": "點",
+    "Runtime.KindVolume": "體積",
+    "Runtime.LineDetail": "長度 = {0}\nΔX = {1}  ΔY = {2}  ΔZ = {3}\n起點 {4}\n終點 {5}",
+    "Runtime.MeasureFailed": "量測失敗：{0}",
+    "Runtime.MeasurementStartCancelled": "已取消目前量測起點（再按 Esc 退出量測模式）",
+    "Runtime.MeasurementsCleared": "已清除全部量測",
+    "Runtime.MeshMeasurementLimited": "此模型無 B-rep（STL/網格），僅支援 點 / 距離 / 角度 / 面距 量測",
+    "Runtime.MeshName": "網格",
+    "Runtime.MeshNameNumbered": "網格 {0}",
+    "Runtime.MeshSurface": "類型 = 網格（無 B-rep）",
+    "Runtime.ModeAlign": "兩點對齊：先點「要移動零件」上的點，再點目標點（純平移，量測會清空）",
+    "Runtime.ModeAlign3": "三點對齊：先在「要移動的檔案」點 3 個特徵點，再到目標檔案點 3 個對應點（旋轉+平移）",
+    "Runtime.ModeAngle": "角度量測：點選第 1 個面（或靠近直線邊）",
+    "Runtime.ModeBrowse": "瀏覽模式（右鍵旋轉、滾輪縮放、中鍵或 Shift+左鍵拖曳平移）",
+    "Runtime.ModeCircle": "圓量測：點擊圓孔內壁或圓邊附近",
+    "Runtime.ModeDistance": "距離量測：點選第 1 點",
+    "Runtime.ModeDrag": "拖曳模式：左鍵按住零件拖動（沿螢幕平面），放開定位；深度方向先轉視角再拖。右鍵仍可轉視角",
+    "Runtime.ModeEdge": "邊量測：點擊靠近要量的邊",
+    "Runtime.ModeFace": "面量測：點擊要量的面",
+    "Runtime.ModeFaceDistance": "面距量測：點選第 1 個面",
+    "Runtime.ModePoint": "點量測：點擊模型表面（自動吸附鄰近頂點）",
+    "Runtime.NoBrep": " · 無 B-rep",
+    "Runtime.NoCircularEdge": "此面沒有圓形邊（請點圓孔內壁或圓邊附近）",
+    "Runtime.NoGeometry": "檔案內沒有可顯示的幾何",
+    "Runtime.NoMeasurableEdge": "此面沒有可量測的邊",
+    "Runtime.NoSurfaceHit": "未命中模型表面",
+    "Runtime.NodeStats": "{0} 實體 · {1} 面 · {2:N0} △",
+    "Runtime.NurbsSurface": "NURBS 曲面",
+    "Runtime.Orthographic": "正交投影（平行投影，適合尺寸確認）",
+    "Runtime.OutlineSize": "\n外形 {0}",
+    "Runtime.ParsingStep": "解析 STEP（大檔可能需數分鐘）…",
+    "Runtime.ParsingStl": "解析 STL（直接讀三角形）…",
+    "Runtime.Perspective": "透視投影",
+    "Runtime.PlaneSurface": "類型 = 平面\n法向量 ({0:F3}, {1:F3}, {2:F3})",
+    "Runtime.Ready": "就緒 — 匯入 STP/STEP/STL/DXF（拖放亦可）。右鍵旋轉、滾輪縮放、中鍵或 Shift+左鍵平移",
+    "Runtime.Removed": "已移除：{0}",
+    "Runtime.RetriedFaces": "、重試補回 {0} 面",
+    "Runtime.Reversed": "（反向）",
+    "Runtime.RevolutionSurface": "旋轉曲面",
+    "Runtime.RootNotFound": "找不到此零件所屬檔案",
+    "Runtime.RotateSelectFile": "請先在樹面板點選要旋轉的檔案（任一節點即可）",
+    "Runtime.Rotated": "已旋轉「{0}」繞 {1} 軸 +90°（再按可繼續轉）",
+    "Runtime.SameFace": "兩次點到同一個面，請點選另一個面",
+    "Runtime.ScreenshotFilter": "PNG 圖片 (*.png)|*.png",
+    "Runtime.ScreenshotSaved": "已儲存截圖 → {0}",
+    "Runtime.ScreenshotTitle": "儲存視圖截圖",
+    "Runtime.SectionCancelled": "已取消 3 點剖面定義",
+    "Runtime.SectionClosed": "剖面已關閉",
+    "Runtime.SectionCollinear": "3點剖面：三點共線，請改選不共線的第 3 點",
+    "Runtime.SectionDefined": "3點剖面：平面已定義（法向 {0:F2}, {1:F2}, {2:F2}）— 用位置滑桿掃剖面",
+    "Runtime.SectionDegenerate": "3點剖面：三點退化（共線），請重新點選",
+    "Runtime.SectionNoHit": "3點剖面：未命中模型表面（已選 {0}/3 點，Esc 取消）",
+    "Runtime.SectionPickPrompt": "3點剖面：請在模型上點 3 個點定義剖切平面（Esc 取消）",
+    "Runtime.SectionPicked": "3點剖面：已選 {0}/3 點",
+    "Runtime.SectionStatus": "剖面：{0} {1:F0}%{2}",
+    "Runtime.ShellName": "殼體",
+    "Runtime.SolidName": "實體",
+    "Runtime.SphericalSurface": "球面",
+    "Runtime.StepExportEmpty": "沒有可匯出的 B-rep 幾何（STEP 匯出僅含 Solid/Shell；請勾選要匯出的 STEP 檔案）",
+    "Runtime.StepExportFailed": "STEP 匯出失敗：{0}",
+    "Runtime.StepExportFilter": "STEP 檔案 (*.stp)|*.stp|STEP 檔案 (*.step)|*.step",
+    "Runtime.StepExportTitle": "匯出目前場景為 STEP（零件在目前對齊位置）",
+    "Runtime.StepExported": "已匯出 STEP（{0} 個實體，目前位置）→ {1}",
+    "Runtime.StepParseFailed": "CADability 無法解析此 STEP 檔",
+    "Runtime.StepParsed": "STEP 解析 {0:N0} ms",
+    "Runtime.StlExportEmpty": "沒有可匯出的網格（請勾選至少一個含實體網格的檔案）",
+    "Runtime.StlExportFailed": "STL 匯出失敗：{0}",
+    "Runtime.StlExportFilter": "STL 檔案 (*.stl)|*.stl",
+    "Runtime.StlExportMergedTitle": "匯出 STL（合併單一檔）",
+    "Runtime.StlExportPerFileTitle": "匯出 STL（每個檔案各一個，以此為基底檔名）",
+    "Runtime.StlExportedMany": "已匯出 {0} 個 STL（共 {1:N0} 三角形）→ {2}",
+    "Runtime.StlExportedOne": "已匯出 STL（{0:N0} 三角形）→ {1}",
+    "Runtime.StlExporting": "匯出 STL 中…",
+    "Runtime.StlNoTriangles": "STL 檔內沒有三角形",
+    "Runtime.StlParsed": "STL 解析 {0:N0} ms（{1} 個網格）",
+    "Runtime.StlRetriangulating": "重新三角化 + 匯出 STL 中…（大組件需要時間）",
+    "Runtime.SurfaceType": "類型 = {0}",
+    "Runtime.ToroidalSurface": "環面",
+    "Runtime.Triangulating": "三角化 {0} 個零件（平行）…",
+    "Runtime.UnitInch": "顯示單位：inch",
+    "Runtime.UnitMillimeter": "顯示單位：mm",
+    "Runtime.UnsupportedFormat": "不支援的格式（支援 .stp / .step / .stl / .dxf；CADability 無 IGES reader）",
+    "Runtime.View": "視圖：{0}",
+    "Runtime.ViewBack": "後",
+    "Runtime.ViewBottom": "下",
+    "Runtime.ViewFront": "前",
+    "Runtime.ViewIso": "等角",
+    "Runtime.ViewLeft": "左",
+    "Runtime.ViewRight": "右",
+    "Runtime.ViewTop": "上",
+    "Runtime.VisibilityInverted": "已反轉顯示",
+    "Runtime.VolumeDetail": "體積 ≈ {0}（網格近似）\n質心 {1}\n外形（AABB）{2} × {3} × {4} {5}",
+    "Runtime.VolumeNoMesh": "「{0}」沒有可計算的面網格（線架構無體積）",
+    "Runtime.VolumeOpenMesh": "「{0}」非封閉網格（開放殼），無法可靠計算體積",
+    "Ui.About.Changelog": "📋  版本紀錄",
+    "Ui.About.Close": "關閉",
+    "Ui.About.Description": "STP / STEP 3D 檢視器。免開重量級 CAD，快速開檔、量測、對齊插合、干涉檢查、剖面、匯出。",
+    "Ui.About.Developer": "👤  開發者",
+    "Ui.About.Email": "電子郵件",
+    "Ui.About.Name": "姓名",
+    "Ui.About.Release010.Change1": "• STEP／STL／DXF 匯入與裝配樹、點／距離／邊／面／圓／角度／面距量測、兩點與三點對齊、干涉檢查、剖面、mm ⇄ inch、CSV 與截圖匯出。",
+    "Ui.About.Release010.Title": "首次釋出",
+    "Ui.About.Release020.Change1": "• 新增拖曳模式：左鍵按住零件直接拖到想要的位置，放開就定位。",
+    "Ui.About.Release020.Change2": "• 0.2.1 修正拖曳過的零件再點擊會當掉的問題。",
+    "Ui.About.Release020.Title": "拖曳模式",
+    "Ui.About.Release030.Change1": "• 新增操作器：選取檔案後出現 XYZ 三色箭頭與旋轉環，箭頭沿軸精確移動、旋轉環繞軸轉任意角度。",
+    "Ui.About.Release030.Title": "三軸操作器",
+    "Ui.About.Release031.Change1": "• 三軸操作器改成永遠浮在畫面最上層，不會被零件擋住，任何角度都抓得到。",
+    "Ui.About.Release031.Title": "操作器永遠可見",
+    "Ui.About.Release032.Change1": "• 修正大型組件（數萬個面）進入量測模式後，轉動視角嚴重卡頓的問題 — 現在量測跟瀏覽一樣順。",
+    "Ui.About.Release032.Title": "大組件量測不再卡",
+    "Ui.About.Release040.Change1": "• 大檔案拉剖面滑桿不再卡住畫面（改到背景計算）。",
+    "Ui.About.Release040.Change2": "• 拖曳／操作器放開零件後的定位計算大幅加速。",
+    "Ui.About.Release040.Change3": "• 程式遇到錯誤會提示訊息並繼續運作，不再整個閃退。",
+    "Ui.About.Release040.Title": "更快、更穩",
+    "Ui.About.Release050.Change1": "• 量距離時點到圓孔邊緣會自動吸到圓心 — 量兩孔中心距（pitch）超方便。",
+    "Ui.About.Release050.Change2": "• 量測快速鍵：P 點、D 距離、E 邊、F 面、C 圓、A 角度、M 面距；Esc 取消。",
+    "Ui.About.Release050.Change3": "• 樹狀面板可搜尋零件名稱；右鍵可「只顯示此節點」隔離觀察，也可以量體積與質心。",
+    "Ui.About.Release050.Change4": "• 新增標準視圖（等角／前／上／右）與正交投影，量尺寸不受透視變形。",
+    "Ui.About.Release050.Change5": "• 剖面新增「3點」模式：在模型上點 3 個點，就能沿任意斜面剖開。",
+    "Ui.About.Release050.Change6": "• 新增匯出 STEP：把對齊好的零件位置存成新 STEP 檔，交接給正式 CAD。",
+    "Ui.About.Release050.Change7": "• 會記住視窗大小、單位設定與最近開啟的 10 個檔案。",
+    "Ui.About.Release050.Title": "量測、視圖、樹狀面板大升級",
+    "Ui.About.Release060.Change1": "• 新增匯出 STL：把畫面上的零件（含對齊、旋轉後的位置）存成 STL 網格檔，可拿去 3D 列印或給其他軟體用。",
+    "Ui.About.Release060.Change2": "• 匯出前會先跳出設定視窗：全部合併成一個檔或每個檔案各存一個、Binary 或文字格式、mm 或 inch、網格精細度 — 確認後才匯出。",
+    "Ui.About.Release060.Change3": "• 設定視窗會即時顯示三角形數量與預估檔案大小。",
+    "Ui.About.Release060.Title": "匯出 STL",
+    "Ui.About.Release070.Change1": "• 上方新增選單列，全部功能依「檔案／視圖／量測／變換／工具」分類，不用再在一長排按鈕裡找。",
+    "Ui.About.Release070.Change2": "• 原本的工具列變成「快速列」：只放常用按鈕。想放哪些自己決定 — 到「快速列 → 自訂按鈕」勾選，下次開啟會記住。",
+    "Ui.About.Release070.Change3": "• 剖面的軸向／位置控制列改成只在開啟剖面時出現，平常不佔空間。",
+    "Ui.About.Release070.Change4": "• 新增「關於」視窗（就是這個畫面），可以看版本紀錄。",
+    "Ui.About.Release070.Title": "介面大整理 — 選單列＋可自訂快速列",
+    "Ui.About.Release071.Change1": "• 開啟大型 STL 網格檔（數十 MB、上百萬三角形）現在幾乎瞬間完成，不用再等好幾分鐘。",
+    "Ui.About.Release071.Change2": "• 例如一個 75 MB、150 萬個三角形的 STL，以前要等到天荒地老，現在不到 1 秒就顯示出來。",
+    "Ui.About.Release071.Title": "大型 STL 秒開",
+    "Ui.About.Technology": ".NET 8 · WPF · C#；CADability（STEP / B-rep 幾何核心）；HelixToolkit（3D 顯示與相機）",
+    "Ui.About.TechnologyTitle": "🔧  技術棧",
+    "Ui.About.Title": "關於 STPViewer",
+    "Ui.Language": "語言",
+    "Ui.Main.3AxisGizmo": "⊹ 三軸操作器",
+    "Ui.Main.3AxisGizmoUseXYZArrows": "三軸操作器：對樹面板選取的檔案顯示 XYZ 箭頭（沿軸移動）與旋轉環（繞軸轉任意角度），每次放開即定位",
+    "Ui.Main.3Point": "🎯 三點",
+    "Ui.Main.3Points": "3點",
+    "Ui.Main.Align": "🎯 對齊",
+    "Ui.Main.Angle": "∠ 角度",
+    "Ui.Main.AngleBetweenFacesStraightEdgesShortcut": "兩面/兩邊夾角（點兩個面或靠近直線邊）— 快速鍵 A",
+    "Ui.Main.AngleBetweenTwoFacesStraightEdges": "兩面/兩邊夾角（點兩個面或靠近直線邊）",
+    "Ui.Main.ApplicationInformationReleaseHistory": "程式資訊與版本紀錄",
+    "Ui.Main.AreaSurfaceTypeNormalVector": "面積 + 曲面類型/法向量",
+    "Ui.Main.AreaSurfaceTypeNormalVectorShortcut": "面積 + 曲面類型/法向量 — 快速鍵 F",
+    "Ui.Main.Capture": "📷 截圖",
+    "Ui.Main.CenterRadiusDiameterCircumference": "圓心/半徑/直徑/周長",
+    "Ui.Main.CenterRadiusDiameterCircumferenceShortcutC": "圓心/半徑/直徑/周長 — 快速鍵 C",
+    "Ui.Main.CheckButtonsShowQuickBarSaved": "勾選要顯示在快速列的常用按鈕（隨設定保存）",
+    "Ui.Main.CheckVisibleModelPairsIntersectionsReport": "2 個以上可見檔案兩兩檢查是否相交；無相交時回報最小間隙",
+    "Ui.Main.ChooseScopeFormatUnitsMeshQuality": "先設定範圍/格式/單位/精度，確認再匯出",
+    "Ui.Main.Circle": "⭕ 圓",
+    "Ui.Main.Clear": "🧹 清除",
+    "Ui.Main.ClearAllMeasurements": "🧹 清除全部量測",
+    "Ui.Main.ClearAllMeasurementsMarkersEscCancels": "清除全部量測與標記（Esc = 取消進行中量測/退出模式）",
+    "Ui.Main.ClickChangeColorIncludingChildNodes": "點擊換色（含子節點）",
+    "Ui.Main.Close": "✕ 關閉",
+    "Ui.Main.CloseSectionView": "關閉剖面檢視",
+    "Ui.Main.CustomizeButtons": "自訂按鈕",
+    "Ui.Main.DeleteThisMeasurement": "刪除此筆量測",
+    "Ui.Main.DisplayInchesMm": "單位顯示 inch（mm ⇄ in）",
+    "Ui.Main.Distance": "📏 距離",
+    "Ui.Main.DistanceXYZCircleCenterSnappingHole": "兩點距離 + ΔXYZ（點到圓邊會吸圓心 → 可量孔對孔 pitch）— 快速鍵 D",
+    "Ui.Main.DistanceXYZCircularEdgesSnapCenters": "兩點距離 + ΔXYZ（點到圓邊會吸圓心 → 可量孔對孔 pitch）",
+    "Ui.Main.Drag": "🖐 拖曳",
+    "Ui.Main.DragMode": "🖐 拖曳模式",
+    "Ui.Main.DragModeHoldLeftMouseButton": "拖曳模式：左鍵按住零件沿螢幕平面拖動，放開定位（深度方向先轉視角再拖）",
+    "Ui.Main.DragResizePanel": "拖曳調整面板寬度",
+    "Ui.Main.Edge": "📐 邊",
+    "Ui.Main.EdgeLength": "📐 邊長",
+    "Ui.Main.Edges": "邊",
+    "Ui.Main.EscCancelsCurrentMeasurementExitsMode": "Esc = 取消進行中量測/退出模式",
+    "Ui.Main.ExistingMeasurementsUpdateImmediatelyValuesStored": "既有量測即時換算；內部一律存 mm",
+    "Ui.Main.ExportMeasurementResultsCSV": "量測結果匯出 CSV",
+    "Ui.Main.ExportMeasurementsCSV": "💾 匯出量測 CSV…",
+    "Ui.Main.ExportSTEP": "📤 匯出 STEP…",
+    "Ui.Main.ExportSTL": "📐 匯出 STL…",
+    "Ui.Main.ExportStepTooltip": "把可見檔案（目前對齊位置）匯出成新 STEP 檔；不動原始檔",
+    "Ui.Main.Face": "⬛ 面",
+    "Ui.Main.FaceDistance": "⇔ 面距",
+    "Ui.Main.FileF": "檔案(_F)",
+    "Ui.Main.FilterAssemblyTreeByNameDoes": "輸入名稱過濾裝配樹（只影響樹面板顯示，不影響 3D 可見性；清空 = 全顯）",
+    "Ui.Main.Fit": "🔍 全覽",
+    "Ui.Main.FitAllModelsView": "縮放至全部模型",
+    "Ui.Main.Flip": "反向",
+    "Ui.Main.Front": "前",
+    "Ui.Main.FrontView": "前視圖",
+    "Ui.Main.FrontViewLookAlongYZ": "前視圖（-Y 方向看，Z 向上）",
+    "Ui.Main.Gizmo": "⊹ 操作器",
+    "Ui.Main.HelpH": "說明(_H)",
+    "Ui.Main.HoldLeftMouseButtonMovePart": "左鍵按住零件沿螢幕平面拖動，放開定位",
+    "Ui.Main.IAboutSTPViewer": "ℹ 關於 STPViewer…",
+    "Ui.Main.ImportSTPSTEPSTLDXFFiles": "匯入 STP/STEP/STL/DXF（可複選，也可直接拖放到視窗）",
+    "Ui.Main.Interference": "🧩 干涉",
+    "Ui.Main.InterferenceCheck": "🧩 干涉檢查",
+    "Ui.Main.InterferenceCheckTestVisibleModelPairs": "干涉檢查：2 個以上可見檔案兩兩檢查是否相交（match 判定）；無相交時回報最小間隙",
+    "Ui.Main.InvertVisibility": "🔄 反轉顯示",
+    "Ui.Main.Iso": "等角",
+    "Ui.Main.IsometricView": "等角視圖",
+    "Ui.Main.LookAlongXZUp": "+X 方向看，Z 向上",
+    "Ui.Main.LookAlongYZUp": "-Y 方向看，Z 向上",
+    "Ui.Main.LookDownFromZ": "+Z 往下看",
+    "Ui.Main.MeasureM": "量測(_M)",
+    "Ui.Main.MeasurePointCoordinatesSnapsVerticesCircle": "量測點座標（吸附頂點/圓心）",
+    "Ui.Main.MeasureStraightCurvedCircularEdgeLengths": "邊長（直線/曲線/圓弧）",
+    "Ui.Main.MeasureVolumeCentroid": "⚖ 量體積 / 質心",
+    "Ui.Main.Measurements": "量測結果",
+    "Ui.Main.MenuImport": "📂 匯入…",
+    "Ui.Main.ModelsAssemblyTree": "模型 / 裝配樹",
+    "Ui.Main.Ortho": "正交",
+    "Ui.Main.OrthographicProjection": "正交投影",
+    "Ui.Main.OrthographicProjectionAvoidsPerspectiveDistortionClick": "正交投影（平行投影，量尺寸不受透視變形；再按切回透視）",
+    "Ui.Main.ParallelProjectionAvoidsPerspectiveDistortionUncheck": "平行投影，量尺寸不受透視變形；取消勾選切回透視",
+    "Ui.Main.PickPointPartMoveThenPick": "先點要移動零件上的點，再點目標點",
+    "Ui.Main.PickThreePointsMovingModelThen": "先在要移動的檔案點 3 個特徵點，再到目標檔案點 3 個對應點（順序對應）",
+    "Ui.Main.Point": "📍 點",
+    "Ui.Main.PointCoordinates": "📍 點座標",
+    "Ui.Main.PointCoordinatesVertexCircleCenterSnapping": "量測點座標（吸附頂點/圓心）— 快速鍵 P",
+    "Ui.Main.QuickBarQ": "快速列(_Q)",
+    "Ui.Main.RecentFiles": "最近檔案",
+    "Ui.Main.RecentlyOpenedFiles": "最近開啟的檔案",
+    "Ui.Main.RemoveThisFile": "移除此檔案",
+    "Ui.Main.RestoreDefaultButtons": "恢復預設按鈕",
+    "Ui.Main.Right": "右",
+    "Ui.Main.RightView": "右視圖",
+    "Ui.Main.RightViewLookAlongXZ": "右視圖（+X 方向看，Z 向上）",
+    "Ui.Main.Rotate90AroundX": "↻ 繞 X 軸 +90°",
+    "Ui.Main.Rotate90AroundY": "↻ 繞 Y 軸 +90°",
+    "Ui.Main.Rotate90AroundZ": "↻ 繞 Z 軸 +90°",
+    "Ui.Main.RotateModelSelectedTree90Around": "選取的檔案繞 X 軸 +90°（先在樹面板點選檔案）",
+    "Ui.Main.RotateModelSelectedTreeAroundIts": "對樹面板選取的檔案，繞其中心旋轉（先在樹面板點選檔案）",
+    "Ui.Main.RotateSelectedModel90AroundY": "選取的檔案繞 Y 軸 +90°",
+    "Ui.Main.RotateSelectedModel90AroundZ": "選取的檔案繞 Z 軸 +90°",
+    "Ui.Main.SavePNGScreenshot3DView2": "3D 視圖截圖存 PNG（2x 解析度）",
+    "Ui.Main.SaveViewPNG": "📷 視圖截圖 PNG…",
+    "Ui.Main.SectionAxis3PointsDefineAn": "剖切軸向（3點 = 在模型上點 3 點定義任意平面）",
+    "Ui.Main.SectionLabel": "✂ 剖面：",
+    "Ui.Main.SectionPosition0100EnterValue": "剖面位置 %（0–100，可直接輸入，離開欄位生效）",
+    "Ui.Main.SectionPositionAlongNormal": "剖面位置（沿法向 %）",
+    "Ui.Main.SectionView": "✂ 剖面檢視",
+    "Ui.Main.ShortestDistanceBetweenFacesMeshApproximation": "面到面最短距離（網格近似）",
+    "Ui.Main.ShortestFaceDistanceMeshApproximationShortcut": "面到面最短距離（網格近似）— 快速鍵 M",
+    "Ui.Main.ShowAll": "☀ 全部顯示",
+    "Ui.Main.ShowHideIncludingChildNodes": "顯示 / 隱藏（含子節點）",
+    "Ui.Main.ShowOnlyThisNode": "👁 只顯示此節點",
+    "Ui.Main.ShowOutlineEdgesManyEdgesCan": "顯示輪廓邊線（邊線量大時轉動視角會變慢）",
+    "Ui.Main.ShowSectionControlsAxisPositionDirection": "開啟後下方出現剖面參數列（軸向/位置/反向）",
+    "Ui.Main.ShowXYZArrowsRotationRingsSelected": "對樹面板選取的檔案顯示 XYZ 箭頭與旋轉環，每次放開即定位",
+    "Ui.Main.StraightCurvedCircularEdgeLengthShortcut": "邊長（直線/曲線/圓弧）— 快速鍵 E",
+    "Ui.Main.SwitchDisplayUnitsBetweenMmInches": "切換顯示單位 mm ⇄ inch（既有量測即時換算）",
+    "Ui.Main.SwitchRetainedSide": "切換保留側",
+    "Ui.Main.ThreePointAlignmentPickThreePoints": "三點對齊（旋轉+平移）：先在要移動的檔案點 3 個特徵點，再到目標檔案點 3 個對應點（順序對應）",
+    "Ui.Main.ThreePointAlignmentRotateTranslate": "🎯 三點對齊（旋轉+平移）",
+    "Ui.Main.ToggleSectionViewItsControls": "開啟/關閉剖面檢視（開啟後下方出現參數列）",
+    "Ui.Main.ToolbarExportStepTooltip": "把可見檔案（目前對齊位置）匯出成新 STEP 檔 — 對齊插合結果可交接 CAD；不動原始檔",
+    "Ui.Main.ToolbarExportStlTooltip": "把可見檔案（目前位置）匯出成 STL 網格檔 — 先設定範圍/格式/單位/精度，確認再匯出",
+    "Ui.Main.ToolbarImport": "📂 匯入",
+    "Ui.Main.ToolbarSection": "✂ 剖面",
+    "Ui.Main.ToolsL": "工具(_L)",
+    "Ui.Main.Top": "上",
+    "Ui.Main.TopView": "上視圖",
+    "Ui.Main.TopViewLookDownFromZ": "上視圖（+Z 往下看）",
+    "Ui.Main.TransformT": "變換(_T)",
+    "Ui.Main.TwoPointAlignmentPickPointMoving": "兩點對齊（平移零件）：先點要移動零件上的點，再點目標點",
+    "Ui.Main.TwoPointAlignmentTranslate": "🎯 兩點對齊（平移）",
+    "Ui.Main.TwoPointDistance": "📏 兩點距離",
+    "Ui.Main.ViewV": "視圖(_V)",
+    "Ui.Main.WindowTitle": "STPViewer — STP/STEP 3D 檢視器",
+    "Ui.Main.ZoomFit": "🔍 縮放至全部",
+    "Ui.Main.ZoomThisNode": "縮放至此節點",
+    "Ui.StlExport.Cancel": "取消",
+    "Ui.StlExport.CustomScaleTooltip": "座標乘上此係數（例：0.001 = mm→m）",
+    "Ui.StlExport.EstimatedSize": "預估 {0}",
+    "Ui.StlExport.EstimatedSizeFine": "以目前網格預估 {0}（實際依重新三角化結果）",
+    "Ui.StlExport.Export": "匯出…",
+    "Ui.StlExport.Format": "格式",
+    "Ui.StlExport.FormatAscii": "ASCII（文字可讀，檔案約 4 倍大）",
+    "Ui.StlExport.FormatBinary": "Binary（建議，檔案小）",
+    "Ui.StlExport.MeshQuality": "網格精度",
+    "Ui.StlExport.QualityCurrent": "目前顯示網格（快，與畫面一致）",
+    "Ui.StlExport.QualityFine": "精細 — 重新三角化，曲面更平滑（慢、檔案大）",
+    "Ui.StlExport.QualityTooltip": "精細會由 B-rep 重新三角化（僅 STEP 來源；STL/DXF 維持現有網格），大組件需要時間",
+    "Ui.StlExport.Scope": "匯出範圍",
+    "Ui.StlExport.ScopeMerge": "全部可見檔案 → 合併成單一 STL",
+    "Ui.StlExport.ScopePerFile": "每個可見檔案 → 各一個 STL",
+    "Ui.StlExport.ScopeTooltip": "STL 無裝配結構；合併 = 所有可見零件進同一檔",
+    "Ui.StlExport.Summary": "{0} 個可見檔案 · {1} 三角形 · {2}",
+    "Ui.StlExport.Title": "匯出 STL — 參數設定",
+    "Ui.StlExport.UnitCustom": "自訂縮放係數…",
+    "Ui.StlExport.UnitInch": "inch（座標 ÷ 25.4）",
+    "Ui.StlExport.UnitMillimeter": "mm（1:1，預設）",
+    "Ui.StlExport.UnitScale": "單位縮放",
+    "Ui.StlExport.UnitTooltip": "STL 檔本身無單位；內部幾何為 mm，選 inch 會把座標 ÷25.4"
+  }
+}
diff --git a/tools/SmokeTest/AlignTest.cs b/tools/SmokeTest/AlignTest.cs
index a1e6c3e..53d440d 100644
--- a/tools/SmokeTest/AlignTest.cs
+++ b/tools/SmokeTest/AlignTest.cs
@@ -1,5 +1,4 @@
-// 三點對齊剛體變換數學驗證：
-// (1) 已知變換還原 (2) Matrix3D ↔ ModOp 兩種表示一致 (3) 共線拒絕
+// Three-point alignment checks: known transform, Matrix3D/ModOp agreement, and collinear rejection.
 using System.Windows.Media.Media3D;
 using STPViewer.Services;
 
@@ -11,29 +10,29 @@ internal static class AlignTest
     {
         int failures = 0;
 
-        // ── (1) 已知剛體變換：繞 Z 軸 90° + 平移 (5,-3,2)，三點求解後應還原同一變換 ──
+        // Recover a known 90-degree Z rotation followed by translation (5,-3,2).
         var truth = Matrix3D.Identity;
         truth.RotateAt(new Quaternion(new Vector3D(0, 0, 1), 90), new Point3D(2, 1, 0));
         truth.Translate(new Vector3D(5, -3, 2));
 
         var p1 = new Point3D(0, 0, 0);
         var p2 = new Point3D(10, 0, 0);
-        var p3 = new Point3D(0, 7, 3);  // 不共線、不在同平面軸上
+        var p3 = new Point3D(0, 7, 3);  // Not collinear with the first two points.
         Point3D q1 = truth.Transform(p1), q2 = truth.Transform(p2), q3 = truth.Transform(p3);
 
         bool ok = RigidAlign.TryRigidTransform(p1, p2, p3, q1, q2, q3, out Matrix3D m);
-        failures += Check("三點求解成功", ok, true);
+        failures += Check("three-point transform solved", ok, true);
 
-        // 三個對應點要精確貼合
+        // Corresponding points must coincide.
         failures += CheckPoint("p1→q1", m.Transform(p1), q1);
         failures += CheckPoint("p2→q2", m.Transform(p2), q2);
         failures += CheckPoint("p3→q3", m.Transform(p3), q3);
 
-        // 剛體變換唯一性：任意第 4 點也應該跟著正確變換
+        // An independent fourth point checks the full rigid transform.
         var r = new Point3D(-4, 12, 8);
-        failures += CheckPoint("任意第4點", m.Transform(r), truth.Transform(r));
+        failures += CheckPoint("fourth point", m.Transform(r), truth.Transform(r));
 
-        // ── (2) ToModOp：CADability ModOp 與 WPF Matrix3D 對同一點要算出同樣結果 ──
+        // CADability ModOp and WPF Matrix3D must transform points identically.
         CADability.ModOp op = RigidAlign.ToModOp(m);
         foreach (Point3D p in new[] { p1, p2, p3, r, new Point3D(1.5, -2.25, 9) })
         {
@@ -42,28 +41,28 @@ internal static class AlignTest
             bool same = Dist(new Point3D(gp.x, gp.y, gp.z), wpf) < 1e-9;
             if (!same)
             {
-                System.Console.WriteLine($"  FAIL: ModOp/Matrix3D 不一致 @ ({p.X},{p.Y},{p.Z})");
+                System.Console.WriteLine($"  FAIL: ModOp/Matrix3D mismatch at ({p.X},{p.Y},{p.Z})");
                 failures++;
             }
         }
-        System.Console.WriteLine($"  {(failures == 0 ? "PASS" : "----")}: ModOp ↔ Matrix3D 一致（5 個測試點）");
+        System.Console.WriteLine($"  {(failures == 0 ? "PASS" : "----")}: ModOp/Matrix3D agree at five points");
 
-        // ── (3) 共線拒絕 ──
+        // Collinear source points must be rejected.
         bool collinearRejected = !RigidAlign.TryRigidTransform(
-            new Point3D(0, 0, 0), new Point3D(1, 0, 0), new Point3D(2, 0, 0), // 共線
+            new Point3D(0, 0, 0), new Point3D(1, 0, 0), new Point3D(2, 0, 0), // Collinear.
             q1, q2, q3, out _);
-        failures += Check("來源共線 → 拒絕", collinearRejected, true);
-        failures += Check("Collinear 判定", RigidAlign.Collinear(
+        failures += Check("collinear source rejected", collinearRejected, true);
+        failures += Check("collinearity detection", RigidAlign.Collinear(
             new Point3D(0, 0, 0), new Point3D(1, 1, 1), new Point3D(3, 3, 3)), true);
 
-        System.Console.WriteLine(failures == 0 ? "AlignTest: 全部通過" : $"AlignTest: {failures} 項失敗");
+        System.Console.WriteLine(failures == 0 ? "AlignTest: all passed" : $"AlignTest: {failures} failed");
         return failures;
     }
 
     private static int Check(string name, bool actual, bool expected)
     {
         bool ok = actual == expected;
-        System.Console.WriteLine($"  {(ok ? "PASS" : "FAIL")}: {name}（{actual}）");
+        System.Console.WriteLine($"  {(ok ? "PASS" : "FAIL")}: {name} ({actual})");
         return ok ? 0 : 1;
     }
 
@@ -71,7 +70,7 @@ internal static class AlignTest
     {
         double d = Dist(actual, expected);
         bool ok = d < 1e-9;
-        System.Console.WriteLine($"  {(ok ? "PASS" : "FAIL")}: {name} 誤差 {d:E2}");
+        System.Console.WriteLine($"  {(ok ? "PASS" : "FAIL")}: {name} error {d:E2}");
         return ok ? 0 : 1;
     }
 
diff --git a/tools/SmokeTest/ClipTest.cs b/tools/SmokeTest/ClipTest.cs
index 0d8cdeb..dcd1236 100644
--- a/tools/SmokeTest/ClipTest.cs
+++ b/tools/SmokeTest/ClipTest.cs
@@ -1,4 +1,4 @@
-// 剖面裁切數學驗證：對單位幾何裁切，檢查保留側與面積守恆
+// Section clipping checks the retained side and triangle area.
 using System.Windows.Media;
 using System.Windows.Media.Media3D;
 using STPViewer.Services;
@@ -11,7 +11,7 @@ internal static class ClipTest
     {
         int failures = 0;
 
-        // 單一三角形 (0,0,0)(10,0,0)(0,10,0)，面積 50
+        // A single triangle with area 50.
         var mesh = new MeshGeometry3D
         {
             Positions = new Point3DCollection
@@ -22,38 +22,38 @@ internal static class ClipTest
         };
         mesh.Freeze();
 
-        // case 1: 平面 x=20，全保留
+        // A plane at x=20 retains the full triangle.
         var m1 = SectionService.ClipMesh(mesh, new Point3D(20, 0, 0), new Vector3D(1, 0, 0));
-        failures += Check("全保留", Area(m1), 50.0);
+        failures += Check("fully retained", Area(m1), 50.0);
 
-        // case 2: 平面 x=-1，全裁掉
+        // A plane at x=-1 removes the full triangle.
         var m2 = SectionService.ClipMesh(mesh, new Point3D(-1, 0, 0), new Vector3D(1, 0, 0));
-        failures += Check("全裁掉", Area(m2), 0.0);
+        failures += Check("fully removed", Area(m2), 0.0);
 
-        // case 3: 平面 x=5 → 保留 x≤5：梯形面積 = 50 - 右側小三角形(底5高5)/2 = 50 - 12.5 = 37.5
+        // At x=5, the retained trapezoid has area 50 - 12.5 = 37.5.
         var m3 = SectionService.ClipMesh(mesh, new Point3D(5, 0, 0), new Vector3D(1, 0, 0));
-        failures += Check("半裁(x≤5)", Area(m3), 37.5);
+        failures += Check("half clipped (x<=5)", Area(m3), 37.5);
         foreach (Point3D p in m3.Positions)
-            if (p.X > 5 + 1e-9) { Console.WriteLine($"  FAIL: 頂點 x={p.X} 超出保留側"); failures++; }
+            if (p.X > 5 + 1e-9) { Console.WriteLine($"  FAIL: vertex x={p.X} is outside retained side"); failures++; }
 
-        // case 4: 反向（保留 x≥5）→ 12.5
+        // Reverse the plane normal to retain the smaller triangle.
         var m4 = SectionService.ClipMesh(mesh, new Point3D(5, 0, 0), new Vector3D(-1, 0, 0));
-        failures += Check("半裁(x≥5)", Area(m4), 12.5);
+        failures += Check("half clipped (x>=5)", Area(m4), 12.5);
 
-        // case 5: 線段裁切
+        // Clip a line segment.
         var segs = new Point3DCollection { new(0, 0, 0), new(10, 0, 0) };
         Point3DCollection s1 = SectionService.ClipSegments(segs, new Point3D(4, 0, 0), new Vector3D(1, 0, 0));
         double segLen = s1.Count == 2 ? (s1[1] - s1[0]).Length : -1;
-        failures += Check("線段裁切長度", segLen, 4.0);
+        failures += Check("clipped segment length", segLen, 4.0);
 
-        Console.WriteLine(failures == 0 ? "ClipTest: 全部通過" : $"ClipTest: {failures} 項失敗");
+        Console.WriteLine(failures == 0 ? "ClipTest: all passed" : $"ClipTest: {failures} failed");
         return failures;
     }
 
     private static int Check(string name, double actual, double expected)
     {
         bool ok = Math.Abs(actual - expected) < 1e-9;
-        Console.WriteLine($"  {(ok ? "PASS" : "FAIL")}: {name} = {actual}（期望 {expected}）");
+        Console.WriteLine($"  {(ok ? "PASS" : "FAIL")}: {name} = {actual} (expected {expected})");
         return ok ? 0 : 1;
     }
 
diff --git a/tools/SmokeTest/ExportTest.cs b/tools/SmokeTest/ExportTest.cs
index 5ec0a6b..29ac70a 100644
--- a/tools/SmokeTest/ExportTest.cs
+++ b/tools/SmokeTest/ExportTest.cs
@@ -5,13 +5,13 @@ using System.Linq;
 using CADability;
 using CADability.GeoObject;
 using STPViewer.Services;
-using IOPath = System.IO.Path; // CADability.GeoObject.Path（曲線）撞名
+using IOPath = System.IO.Path; // Avoid the CADability.GeoObject.Path name collision.
 
 namespace SmokeTest;
 
 /// <summary>
-/// STEP 匯出往返驗證（v0.5.0 匯出 STEP 功能的無 UI 驗證）：
-/// 匯入來源 STEP → 走與 MainViewModel.ExportStepFile 相同路徑寫出新檔 → 重新匯入比對實體數。
+/// Headless STEP export round trip: import, export through the same CADability path,
+/// then import the result and compare solid counts.
 /// </summary>
 public static class ExportTest
 {
@@ -20,26 +20,26 @@ public static class ExportTest
         Console.WriteLine($"=== ExportTest: {IOPath.GetFileName(sourcePath)} → {IOPath.GetFileName(outPath)} ===");
         ImportedFileData data = new StepImportService().Import(sourcePath);
         var geos = Collect(data.Root).Where(g => g is Solid or Shell).ToList();
-        Console.WriteLine($"  來源 Solid/Shell 物件 = {geos.Count}（Solids = {data.Root.SolidCount}）");
+        Console.WriteLine($"  Source Solid/Shell objects = {geos.Count} (solids = {data.Root.SolidCount})");
 
         Project project = Project.CreateSimpleProject();
         Model model = project.GetActiveModel();
         foreach (IGeoObject g in geos) model.Add(g);
         new ExportStep().WriteToFile(outPath, project);
         var fi = new FileInfo(outPath);
-        Console.WriteLine($"  已寫出（{fi.Length:N0} bytes）");
+        Console.WriteLine($"  Written ({fi.Length:N0} bytes)");
         if (fi.Length < 100)
         {
-            Console.WriteLine("ExportTest: FAIL（輸出檔近乎空白）");
+            Console.WriteLine("ExportTest: FAIL (output is nearly empty)");
             return 1;
         }
 
         ImportedFileData back = new StepImportService().Import(outPath);
-        Console.WriteLine($"  回讀 Solids = {back.Root.SolidCount}, Faces = {back.Root.FaceCount}");
+        Console.WriteLine($"  Reimported solids = {back.Root.SolidCount}, faces = {back.Root.FaceCount}");
         bool ok = back.Root.SolidCount == data.Root.SolidCount && back.Root.FaceCount > 0;
         Console.WriteLine(ok
-            ? "ExportTest: PASS（實體數一致）"
-            : $"ExportTest: FAIL（來源 Solids {data.Root.SolidCount} ↔ 回讀 {back.Root.SolidCount}）");
+            ? "ExportTest: PASS (solid counts match)"
+            : $"ExportTest: FAIL (source solids {data.Root.SolidCount} vs reimported {back.Root.SolidCount})");
         return ok ? 0 : 1;
     }
 
diff --git a/tools/SmokeTest/InterferenceTest.cs b/tools/SmokeTest/InterferenceTest.cs
index d459604..448de73 100644
--- a/tools/SmokeTest/InterferenceTest.cs
+++ b/tools/SmokeTest/InterferenceTest.cs
@@ -1,4 +1,4 @@
-// 干涉檢查數學驗證：相交 / 分離 / 貼合三種情境
+// Interference checks for intersecting, separated, and touching meshes.
 using System.Windows.Media;
 using System.Windows.Media.Media3D;
 using STPViewer.Services;
@@ -11,41 +11,41 @@ internal static class InterferenceTest
     {
         int failures = 0;
 
-        // 兩個互穿的四面體（B 比 A 平移 +5，邊長 10 → 必相交）
+        // Two tetrahedra overlap when B is offset by 5 along X.
         MeshGeometry3D a = Tetra(new Vector3D(0, 0, 0));
         MeshGeometry3D b = Tetra(new Vector3D(5, 0, 0));
         InterferenceResult r1 = InterferenceService.Check(new[] { a }, new[] { b });
-        failures += Check("互穿 → 相交", r1.Intersects, true);
-        failures += Check("互穿 → 有交線段", r1.Segments.Count > 0, true);
+        failures += Check("overlap intersects", r1.Intersects, true);
+        failures += Check("overlap has intersection segments", r1.Segments.Count > 0, true);
 
-        // 分離（B 平移 +30，gap 應 ≈ 30 - 10 = 20）
+        // B at X=30 leaves a gap of about 20.
         MeshGeometry3D c = Tetra(new Vector3D(30, 0, 0));
         InterferenceResult r2 = InterferenceService.Check(new[] { a }, new[] { c });
-        failures += Check("分離 → 不相交", r2.Intersects, false);
+        failures += Check("separated meshes do not intersect", r2.Intersects, false);
         bool gapOk = Math.Abs(r2.GapDistance - 20.0) < 0.01;
-        Console.WriteLine($"  {(gapOk ? "PASS" : "FAIL")}: 分離 gap = {r2.GapDistance:F4}（期望 ≈ 20）");
+        Console.WriteLine($"  {(gapOk ? "PASS" : "FAIL")}: separated gap = {r2.GapDistance:F4} (expected ~20)");
         if (!gapOk) failures++;
 
-        // 貼合（B 平移 +10，頂點剛好接觸 → 不算穿透、gap ≈ 0）
+        // B at X=10 touches a vertex without penetrating A.
         MeshGeometry3D d = Tetra(new Vector3D(10, 0, 0));
         InterferenceResult r3 = InterferenceService.Check(new[] { a }, new[] { d });
-        failures += Check("貼合 → 不算穿透", r3.Intersects, false);
+        failures += Check("touching is not penetration", r3.Intersects, false);
         bool touchOk = r3.GapDistance < 0.01;
-        Console.WriteLine($"  {(touchOk ? "PASS" : "FAIL")}: 貼合 gap = {r3.GapDistance:F6}（期望 ≈ 0）");
+        Console.WriteLine($"  {(touchOk ? "PASS" : "FAIL")}: touching gap = {r3.GapDistance:F6} (expected ~0)");
         if (!touchOk) failures++;
 
-        Console.WriteLine(failures == 0 ? "InterferenceTest: 全部通過" : $"InterferenceTest: {failures} 項失敗");
+        Console.WriteLine(failures == 0 ? "InterferenceTest: all passed" : $"InterferenceTest: {failures} failed");
         return failures;
     }
 
     private static int Check(string name, bool actual, bool expected)
     {
         bool ok = actual == expected;
-        Console.WriteLine($"  {(ok ? "PASS" : "FAIL")}: {name}（{actual}）");
+        Console.WriteLine($"  {(ok ? "PASS" : "FAIL")}: {name} ({actual})");
         return ok ? 0 : 1;
     }
 
-    /// <summary>邊長 10 的四面體，offset 平移</summary>
+    /// <summary>A tetrahedron with side length 10, translated by offset.</summary>
     private static MeshGeometry3D Tetra(Vector3D offset)
     {
         Point3D P(double x, double y, double z) => new Point3D(x, y, z) + offset;
diff --git a/tools/SmokeTest/LocalizationTest.cs b/tools/SmokeTest/LocalizationTest.cs
new file mode 100644
index 0000000..134d8fb
--- /dev/null
+++ b/tools/SmokeTest/LocalizationTest.cs
@@ -0,0 +1,313 @@
+using System.ComponentModel;
+using System.Globalization;
+using System.IO;
+using System.Reflection;
+using System.Text.Json;
+using System.Text.RegularExpressions;
+using System.Windows.Media.Media3D;
+using CADability.GeoObject;
+using STPViewer.Models;
+using STPViewer.Services;
+using STPViewer.ViewModels;
+using IOPath = System.IO.Path;
+
+namespace SmokeTest;
+
+internal static class LocalizationTest
+{
+    private static readonly Regex FormatIndex = new(@"(?<!\{)\{(\d+)(?:[^{}]*)\}(?!\})", RegexOptions.Compiled);
+
+    public static int Run()
+    {
+        int failures = 0;
+        Exception? error = null;
+        var thread = new Thread(() =>
+        {
+            try { failures = RunCore(); }
+            catch (Exception ex) { error = ex; }
+        });
+        thread.SetApartmentState(ApartmentState.STA);
+        thread.Start();
+        thread.Join();
+        if (error is not null)
+        {
+            Console.WriteLine($"LocalizationTest: {error}");
+            return 1;
+        }
+        return failures;
+    }
+
+    private static int RunCore()
+    {
+        int failures = CheckTemporaryPacks() + CheckBundledPacks() + CheckViewModel() + CheckSettings();
+        Console.WriteLine(failures == 0 ? "LocalizationTest: all passed" : $"LocalizationTest: {failures} failed");
+        return failures;
+    }
+
+    private static int CheckTemporaryPacks()
+    {
+        int failures = 0;
+        string directory = IOPath.Combine(IOPath.GetTempPath(), "stpviewer_i18n_" + Guid.NewGuid().ToString("N"));
+        try
+        {
+            failures += Check("missing directory loads without languages", new LocalizationService(directory).Languages.Count == 0);
+            Directory.CreateDirectory(directory);
+            failures += Check("empty directory loads without languages", new LocalizationService(directory).Languages.Count == 0);
+            WritePack(directory, "en", "English", new()
+            {
+                ["Ui.Sample"] = "View", ["Ui.Fallback"] = "Fallback {0}",
+                ["Ui.BadBrace"] = "English {0}", ["Ui.BadIndex"] = "English {0}",
+                ["Ui.BothBad"] = "English {"
+            });
+            WritePack(directory, "zh_cn", "Simplified", new()
+            {
+                ["Ui.Sample"] = "CN_VIEW", ["Ui.BadBrace"] = "Chinese {",
+                ["Ui.BadIndex"] = "Chinese {1}", ["Ui.BothBad"] = "Chinese {"
+            });
+            WritePack(directory, "zh_tw", "Traditional", new() { ["Ui.Sample"] = "TW_VIEW" });
+            WritePack(directory, "pirate_dialect", "Pirate", new() { ["Ui.Sample"] = "ARR_VIEW" });
+            File.WriteAllText(IOPath.Combine(directory, "broken.json"), "{invalid json");
+            File.WriteAllText(IOPath.Combine(directory, "no_key.json"), "{\"data\":{\"Ui.Sample\":\"unused\"}}");
+            File.WriteAllText(IOPath.Combine(directory, "no_data.json"), "{\"key\":\"Missing data\"}");
+            File.WriteAllText(IOPath.Combine(directory, "non_string.json"), "{\"key\":\"Invalid\",\"data\":{\"Ui.Sample\":42}}");
+
+            CultureInfo oldUi = CultureInfo.CurrentUICulture;
+            LocalizationService service;
+            try
+            {
+                CultureInfo.CurrentUICulture = CultureInfo.GetCultureInfo("en-US");
+                service = new LocalizationService(directory);
+            }
+            finally { CultureInfo.CurrentUICulture = oldUi; }
+
+            failures += Check("valid packs isolated from malformed files", service.Languages.Count == 4 &&
+                service.Languages.Select(l => l.Id).Order().SequenceEqual(new[] { "en", "pirate_dialect", "zh_cn", "zh_tw" }));
+            failures += Check("display names and data loaded", service.Languages.Any(l =>
+                l.Id == "pirate_dialect" && l.Key == "Pirate" && l.Data["Ui.Sample"] == "ARR_VIEW"));
+            failures += Check("English selected from system culture", service.Language == "en");
+            failures += Check("legacy Chinese IDs resolved", service.ResolveLanguage("zh-CN") == "zh_cn" &&
+                service.ResolveLanguage("zh-TW") == "zh_tw");
+            failures += Check("Chinese script and region aliases resolved", service.ResolveLanguage("zh-Hans") == "zh_cn" &&
+                service.ResolveLanguage("zh-SG") == "zh_cn" && service.ResolveLanguage("zh-Hant") == "zh_tw" &&
+                service.ResolveLanguage("zh-HK") == "zh_tw" && service.ResolveLanguage("zh-MO") == "zh_tw");
+            failures += Check("custom language ID resolved", service.ResolveLanguage("pirate-dialect") == "pirate_dialect");
+            failures += Check("unknown language falls back", service.ResolveLanguage("unknown") == "en");
+            failures += Check("invalid custom ID falls back", service.ResolveLanguage("pirate_other") == "en");
+
+            CultureInfo beforeNull = CultureInfo.CurrentUICulture;
+            try
+            {
+                CultureInfo.CurrentUICulture = CultureInfo.GetCultureInfo("zh-HK");
+                failures += Check("null language uses system UI culture", service.ResolveLanguage(null) == "zh_tw");
+            }
+            finally { CultureInfo.CurrentUICulture = beforeNull; }
+
+            LanguageDefinition chinese = service.Languages.Single(l => l.Id == "zh_cn");
+            bool selectedNotified = false, indexerNotified = false;
+            chinese.PropertyChanged += (_, e) => selectedNotified |= e.PropertyName == nameof(LanguageDefinition.IsSelected);
+            ((INotifyPropertyChanged)service).PropertyChanged += (_, e) => indexerNotified |= e.PropertyName == "Item[]";
+            service.SetLanguage("zh-CN");
+            failures += Check("selection and indexer notify", service.Language == "zh_cn" &&
+                chinese.IsSelected && selectedNotified && indexerNotified);
+            failures += Check("selected data and fallback", service["Ui.Sample"] == "CN_VIEW" &&
+                service["Ui.Fallback"] == "Fallback {0}" && service["Ui.Missing"] == "Ui.Missing");
+            failures += Check("malformed brace uses English format", service.FormatText("Ui.BadBrace", "value") == "English value");
+            failures += Check("missing format argument uses English format", service.FormatText("Ui.BadIndex", "value") == "English value");
+            failures += Check("invalid English format returns key", service.FormatText("Ui.BothBad", "value") == "Ui.BothBad");
+            service.SetLanguage("pirate_dialect");
+            failures += Check("custom language selected", service.Language == "pirate_dialect" &&
+                service["Ui.Sample"] == "ARR_VIEW");
+
+            WritePack(directory, "new_language", "New language", new() { ["Ui.Sample"] = "NEW_VIEW" });
+            WritePack(directory, "en", "English", new() { ["Ui.Sample"] = "Updated view", ["Ui.Fallback"] = "Fallback {0}" });
+            failures += Check("existing instance does not hot reload", service.Languages.Count == 4 &&
+                service.Languages.Single(l => l.Id == "en").Data["Ui.Sample"] == "View");
+            var reloaded = new LocalizationService(directory);
+            failures += Check("new instance rescans files and values", reloaded.Languages.Count == 5 &&
+                reloaded.Languages.Single(l => l.Id == "en").Data["Ui.Sample"] == "Updated view");
+
+            File.Delete(IOPath.Combine(directory, "zh_tw.json"));
+            var withoutTraditional = new LocalizationService(directory);
+            failures += Check("missing language not listed", withoutTraditional.Languages.All(l => l.Id != "zh_tw"));
+            failures += Check("missing legacy ID falls back", withoutTraditional.ResolveLanguage("zh-TW") == "en");
+        }
+        finally
+        {
+            if (Directory.Exists(directory)) Directory.Delete(directory, recursive: true);
+        }
+        return failures;
+    }
+
+    private static void WritePack(string directory, string id, string name, Dictionary<string, string> data) =>
+        File.WriteAllText(IOPath.Combine(directory, id + ".json"), JsonSerializer.Serialize(new { key = name, data }));
+
+    private static int CheckBundledPacks()
+    {
+        int failures = 0;
+        LocalizationService service = LocalizationService.Instance;
+        failures += Check("bundled languages available", new[] { "en", "zh_cn", "zh_tw" }
+            .All(id => service.Languages.Any(l => l.Id == id)));
+        LanguageDefinition? english = service.Languages.FirstOrDefault(l => l.Id == "en");
+        if (english is null) return failures;
+        failures += Check("bundled English data nonempty", english.Data.Count > 0 &&
+            english.Data.Values.All(v => !string.IsNullOrWhiteSpace(v)));
+        int formatFailures = 0;
+        foreach (LanguageDefinition language in service.Languages)
+            foreach ((string key, string value) in language.Data)
+            {
+                if (string.IsNullOrWhiteSpace(value)) formatFailures++;
+                int[] indices = Indices(value);
+                if (english.Data.TryGetValue(key, out string? fallback) && !Indices(fallback).SequenceEqual(indices))
+                {
+                    Console.WriteLine($"  FAIL: {language.Id} format arguments differ for {key}");
+                    formatFailures++;
+                }
+                object[] args = Enumerable.Range(0, indices.DefaultIfEmpty(-1).Max() + 1)
+                    .Select(i => (object)i).ToArray();
+                try { _ = string.Format(CultureInfo.InvariantCulture, value, args); }
+                catch (FormatException)
+                {
+                    Console.WriteLine($"  FAIL: {language.Id} format syntax for {key}");
+                    formatFailures++;
+                }
+            }
+        failures += Check("bundled data and format strings valid", formatFailures == 0);
+        failures += Check("missing key returns key", service["__missing_localization_key__"] == "__missing_localization_key__");
+        return failures;
+    }
+
+    private static int CheckViewModel()
+    {
+        int failures = 0;
+        LocalizationService service = LocalizationService.Instance;
+        string originalLanguage = service.Language;
+        CultureInfo numericCulture = CultureInfo.CurrentCulture;
+        try
+        {
+            service.SetLanguage("en");
+            var vm = new MainViewModel();
+            vm.InitializeLocalization();
+            try
+            {
+                string oldLabel = vm.QuickBar["Import"].Label;
+                bool labelChanged = false;
+                vm.QuickBar["Import"].PropertyChanged += (_, e) =>
+                    labelChanged |= e.PropertyName == nameof(QuickBarItemViewModel.Label);
+
+                MeasurementResult result = new MeasurementService().MeasureDistance(
+                    new Point3D(0, 0, 0), new Point3D(25.4, 0, 0), "D1", 0.2);
+                vm.Measurements.Add(result);
+                vm.UseInch = true;
+                string oneInch = 1d.ToString("F4", numericCulture) + " in";
+                string beforeTitle = result.Title, beforeDetail = result.Detail;
+                string beforeLabel = result.DynamicLabels.Single().Label.Text;
+                var (distanceLabel, distanceTextFor) = result.DynamicLabels.Single();
+                int labelRefreshes = 0;
+                result.DynamicLabels[0] = (distanceLabel, u =>
+                {
+                    labelRefreshes++;
+                    return distanceTextFor(u);
+                });
+                bool titleChanged = false, detailChanged = false;
+                result.PropertyChanged += (_, e) =>
+                {
+                    titleChanged |= e.PropertyName == nameof(MeasurementResult.Title);
+                    detailChanged |= e.PropertyName == nameof(MeasurementResult.Detail);
+                };
+
+                vm.ChangeLanguageCommand.Execute("zh_tw");
+                failures += Check("VM selects language", service.Language == "zh_tw" &&
+                    service.Languages.Single(l => l.Id == "zh_tw").IsSelected);
+                failures += Check("existing distance detail translated", beforeDetail != result.Detail &&
+                    titleChanged && detailChanged && result.Detail.Contains(oneInch, StringComparison.Ordinal));
+                failures += Check("distance and number culture preserved", vm.UseInch &&
+                    CultureInfo.CurrentCulture.Equals(numericCulture) && beforeTitle == result.Title &&
+                    result.Title.Contains(oneInch, StringComparison.Ordinal));
+                failures += Check("3D distance label refreshed", labelRefreshes == 1 &&
+                    beforeLabel == oneInch && result.DynamicLabels.Single().Label.Text == beforeLabel);
+                failures += Check("quick bar label refreshed", labelChanged && vm.QuickBar["Import"].Label != oldLabel);
+
+                LanguageDefinition selected = service.Languages.Single(l => l.Id == "zh_tw");
+                bool reselected = false;
+                selected.PropertyChanged += (_, e) => reselected |= e.PropertyName == nameof(LanguageDefinition.IsSelected);
+                vm.ChangeLanguageCommand.Execute("zh_tw");
+                failures += Check("reselecting current language restores check", reselected && selected.IsSelected);
+            }
+            finally { vm.DisposeLocalization(); }
+            failures += CheckImportedNames(service);
+        }
+        finally { service.SetLanguage(originalLanguage); }
+        return failures;
+    }
+
+    private static int CheckImportedNames(LocalizationService service)
+    {
+        int failures = 0;
+        MethodInfo blockNode = typeof(StepImportService).GetMethod("BlockNode", BindingFlags.NonPublic | BindingFlags.Instance)!;
+        var importer = new StepImportService();
+        service.SetLanguage("en");
+
+        ImportedNode Import(Block block) => (ImportedNode)blockNode.Invoke(importer, [block])!;
+        var namedSolidBlock = Block.Construct();
+        namedSolidBlock.Name = "Solid";
+        namedSolidBlock.Add(Solid.Construct());
+        ImportedNode namedSolid = Import(namedSolidBlock);
+        var namedShellBlock = Block.Construct();
+        namedShellBlock.Name = "Shell";
+        namedShellBlock.Add(Shell.Construct());
+        ImportedNode namedShell = Import(namedShellBlock);
+        var defaultSolidBlock = Block.Construct();
+        defaultSolidBlock.Add(Solid.Construct());
+        ImportedNode defaultSolid = Import(defaultSolidBlock);
+        var defaultShellBlock = Block.Construct();
+        defaultShellBlock.Add(Shell.Construct());
+        ImportedNode defaultShellLeaf = Import(defaultShellBlock).Children.Single();
+        var collisionBlock = Block.Construct();
+        var realComponentShell = Shell.Construct();
+        realComponentShell.Name = "Component";
+        collisionBlock.Add(realComponentShell);
+        ImportedNode collision = Import(collisionBlock);
+
+        ModelNodeViewModel ViewModel(ImportedNode node) => new(0)
+        {
+            Name = node.Name,
+            NameKey = node.NameKey,
+            NameNumber = node.NameNumber
+        };
+        var namedSolidVm = ViewModel(namedSolid);
+        var namedShellVm = ViewModel(namedShell);
+        var defaultSolidVm = ViewModel(defaultSolid);
+        var defaultShellVm = ViewModel(defaultShellLeaf);
+        var collisionVm = ViewModel(collision);
+        service.SetLanguage("zh_cn");
+        failures += Check("explicit solid name retained", namedSolid.NameKey is null && namedSolidVm.Name == "Solid");
+        failures += Check("real block name retained", namedShell.NameKey is null && namedShellVm.Name == "Shell");
+        failures += Check("default solid name translated", defaultSolid.NameKey == "Runtime.SolidName" &&
+            defaultSolidVm.Name == service["Runtime.SolidName"]);
+        failures += Check("default shell name translated", defaultShellLeaf.NameKey == "Runtime.ShellName" &&
+            defaultShellVm.Name == service["Runtime.ShellName"]);
+        failures += Check("real child name wins collision", collision.NameKey is null && collisionVm.Name == "Component");
+        return failures;
+    }
+
+    private static int CheckSettings()
+    {
+        var settings = new AppSettings
+        {
+            Language = "zh-CN", WindowWidth = 1200, WindowHeight = 800, WindowLeft = 100, WindowTop = 100
+        };
+        AppSettings? restored = JsonSerializer.Deserialize<AppSettings>(JsonSerializer.Serialize(settings));
+        return Check("legacy ID round trips through settings JSON", restored?.Language == "zh-CN" &&
+            LocalizationService.Instance.ResolveLanguage(restored.Language) == "zh_cn");
+    }
+
+    private static int[] Indices(string format) => FormatIndex.Matches(format)
+        .Select(m => int.Parse(m.Groups[1].Value, CultureInfo.InvariantCulture))
+        .Distinct().Order().ToArray();
+
+    private static int Check(string name, bool ok)
+    {
+        Console.WriteLine($"  {(ok ? "PASS" : "FAIL")}: {name}");
+        return ok ? 0 : 1;
+    }
+}
diff --git a/tools/SmokeTest/MakeDxf.cs b/tools/SmokeTest/MakeDxf.cs
index 39678a1..496222f 100644
--- a/tools/SmokeTest/MakeDxf.cs
+++ b/tools/SmokeTest/MakeDxf.cs
@@ -1,4 +1,4 @@
-// 測試輔助：用 CADability 內嵌的 netDxf 產生標準 DXF 測試檔
+// Generate a small standard DXF test file with the bundled netDxf library.
 using netDxf;
 using netDxf.Entities;
 
@@ -12,6 +12,6 @@ internal static class MakeDxf
         doc.Entities.Add(new Line(new Vector3(0, 0, 0), new Vector3(100, 50, 0)));
         doc.Entities.Add(new Circle(new Vector3(50, 25, 0), 10));
         doc.Save(path);
-        Console.WriteLine($"已產生 {path}");
+        Console.WriteLine($"Generated {path}");
     }
 }
diff --git a/tools/SmokeTest/MakeStl.cs b/tools/SmokeTest/MakeStl.cs
index c9f75b4..6601516 100644
--- a/tools/SmokeTest/MakeStl.cs
+++ b/tools/SmokeTest/MakeStl.cs
@@ -2,12 +2,12 @@ using System.IO;
 
 namespace SmokeTest;
 
-/// <summary>產生測試用 binary STL：一片 gridN×gridN 的網格，每格 2 個三角形（波浪起伏，避免全共面）。</summary>
+/// <summary>Generate a binary STL grid with two triangles per cell and noncoplanar vertices.</summary>
 internal static class MakeStl
 {
     public static void Run(string path, int triCount)
     {
-        // 每格 2 三角，格數 = triCount/2；邊長 grid = ceil(sqrt(cells))
+        // Two triangles per cell; use a square grid large enough for the requested count.
         int cells = System.Math.Max(1, triCount / 2);
         int grid = (int)System.Math.Ceiling(System.Math.Sqrt(cells));
         int tris = grid * grid * 2;
@@ -36,6 +36,6 @@ internal static class MakeStl
                 WriteTri(bw, x0, y0, Z(x, y), x1, y1, Z(x + 1, y + 1), x0, y1, Z(x, y + 1));
             }
 
-        Console.WriteLine($"寫出 {tris:N0} 三角形 → {path} ({new FileInfo(path).Length:N0} bytes)");
+        Console.WriteLine($"Wrote {tris:N0} triangles to {path} ({new FileInfo(path).Length:N0} bytes)");
     }
 }
diff --git a/tools/SmokeTest/Program.cs b/tools/SmokeTest/Program.cs
index f8583a9..c91283d 100644
--- a/tools/SmokeTest/Program.cs
+++ b/tools/SmokeTest/Program.cs
@@ -1,4 +1,4 @@
-// 無 UI smoke test：驗證 CAD 檔解析 → 三角化 → 裝配樹 整條匯入管線
+// Headless smoke tests for CAD import, triangulation, and the assembly tree.
 using System.Diagnostics;
 using System.IO;
 using STPViewer.Services;
@@ -7,7 +7,7 @@ Console.OutputEncoding = System.Text.Encoding.UTF8;
 
 if (args.Length == 0)
 {
-    Console.WriteLine("用法: SmokeTest [--tree] <file.stp|.stl|.dxf> [...]");
+    Console.WriteLine("Usage: SmokeTest [--tree] <file.stp|.stl|.dxf> [...]");
     return 1;
 }
 
@@ -38,6 +38,9 @@ if (args[0] == "--interference-test")
 if (args[0] == "--align-test")
     return SmokeTest.AlignTest.Run() == 0 ? 0 : 2;
 
+if (args[0] == "--localization-test")
+    return SmokeTest.LocalizationTest.Run() == 0 ? 0 : 2;
+
 if (args[0] == "--bbox")
     return SmokeTest.BBoxDump.Run(args[1]);
 
@@ -47,7 +50,7 @@ if (args[0] == "--export-test")
 if (args[0] == "--stl-export-test")
     return SmokeTest.StlExportTest.Run(args.Length > 1 ? args[1] : null) == 0 ? 0 : 2;
 
-var service = new StepImportService { Progress = s => Console.WriteLine($"  [階段] {s}") };
+var service = new StepImportService { Progress = s => Console.WriteLine($"  [stage] {s}") };
 int failed = 0;
 
 foreach (string path in args)
@@ -64,7 +67,7 @@ foreach (string path in args)
         Console.WriteLine($"  Triangles : {r.TriangleCount:N0}");
         Console.WriteLine($"  Bounds    : {r.Bounds.SizeX:F2} x {r.Bounds.SizeY:F2} x {r.Bounds.SizeZ:F2} mm");
         Console.WriteLine($"  Time      : {sw.ElapsedMilliseconds} ms");
-        Console.WriteLine("  --- 裝配樹 ---");
+        Console.WriteLine("  --- assembly tree ---");
         PrintNode(r, 1);
     }
     catch (Exception ex)
@@ -81,6 +84,6 @@ static void PrintNode(ImportedNode n, int indent)
 {
     string seg = n.EdgeSegments is null ? "" : $", edgeSegs={n.EdgeSegments.Count / 2:N0}";
     Console.WriteLine($"{new string(' ', indent * 2)}{n.Name}  " +
-        $"[solids={n.SolidCount}, faces={n.FaceCount}, tris={n.TriangleCount:N0}{seg}{(n.HasBrep ? "" : ", 無B-rep")}]");
+        $"[solids={n.SolidCount}, faces={n.FaceCount}, tris={n.TriangleCount:N0}{seg}{(n.HasBrep ? "" : ", no B-rep")}]");
     foreach (ImportedNode c in n.Children) PrintNode(c, indent + 1);
 }
diff --git a/tools/SmokeTest/StlExportTest.cs b/tools/SmokeTest/StlExportTest.cs
index 823ec5f..905200b 100644
--- a/tools/SmokeTest/StlExportTest.cs
+++ b/tools/SmokeTest/StlExportTest.cs
@@ -5,15 +5,13 @@ using System.Text;
 using System.Windows.Media;
 using System.Windows.Media.Media3D;
 using STPViewer.Services;
-using IOPath = System.IO.Path; // CADability.GeoObject.Path（曲線）撞名
+using IOPath = System.IO.Path; // Avoid the CADability.GeoObject.Path name collision.
 
 namespace SmokeTest;
 
 /// <summary>
-/// STL 匯出驗證（無 UI）：
-/// 1) binary — 已知立方體網格寫出 → 解析 header/三角形數/座標範圍比對（含縮放）
-/// 2) ASCII — facet 數與 solid/endsolid 結構
-/// 3) 退化三角形（零面積）自動濾除
+/// Headless STL export checks:
+/// binary round trip, ASCII facet structure, and degenerate triangle filtering.
 /// </summary>
 public static class StlExportTest
 {
@@ -24,20 +22,20 @@ public static class StlExportTest
         string dir = IOPath.Combine(IOPath.GetTempPath(), "stpviewer_stl_test");
         Directory.CreateDirectory(dir);
 
-        MeshGeometry3D cube = BuildCube(10); // 10×10×10 mm、12 三角形
+        MeshGeometry3D cube = BuildCube(10); // 10x10x10 mm, 12 triangles.
 
-        // 1) binary：三角形數 + 縮放後座標範圍
+        // Binary triangle count and scaled coordinate range.
         {
             string f = IOPath.Combine(dir, "cube_bin.stl");
-            double scale = 1.0 / 25.4; // mm → inch
+            double scale = 1.0 / 25.4; // mm to inches.
             int written = StlExportService.Write(f, new[] { cube }, ascii: false, scale);
             (uint count, float min, float max) = ReadBinary(f);
             bool ok = written == 12 && count == 12
                       && Math.Abs(min - 0f) < 1e-5 && Math.Abs(max - 10f / 25.4f) < 1e-4;
-            Report(ref failed, ok, $"binary 寫出/回讀 12 三角形、inch 縮放範圍 [{min:F4}, {max:F4}]");
+            Report(ref failed, ok, $"binary round trip: 12 triangles, inch range [{min:F4}, {max:F4}]");
         }
 
-        // 2) ASCII：facet 數 + 結構
+        // ASCII facet count and structure.
         {
             string f = IOPath.Combine(dir, "cube_ascii.stl");
             int written = StlExportService.Write(f, new[] { cube }, ascii: true, scale: 1.0);
@@ -46,15 +44,15 @@ public static class StlExportTest
             bool ok = written == 12 && facets == 12
                       && text.StartsWith("solid ", StringComparison.Ordinal)
                       && text.Contains("endsolid");
-            Report(ref failed, ok, $"ASCII 結構完整、facet = {facets}");
+            Report(ref failed, ok, $"ASCII structure valid, facets = {facets}");
         }
 
-        // 3) 退化三角形濾除：加一個零面積三角形 → 仍是 12
+        // A zero-area triangle must be filtered from the export.
         {
             var degenerate = new MeshGeometry3D();
             degenerate.Positions.Add(new Point3D(0, 0, 0));
             degenerate.Positions.Add(new Point3D(1, 1, 1));
-            degenerate.Positions.Add(new Point3D(2, 2, 2)); // 共線 → 面積 0
+            degenerate.Positions.Add(new Point3D(2, 2, 2)); // Collinear: zero area.
             degenerate.TriangleIndices.Add(0);
             degenerate.TriangleIndices.Add(1);
             degenerate.TriangleIndices.Add(2);
@@ -64,17 +62,16 @@ public static class StlExportTest
             int written = StlExportService.Write(f, new[] { cube, degenerate }, ascii: false, scale: 1.0);
             (uint count, _, _) = ReadBinary(f);
             bool ok = written == 12 && count == 12;
-            Report(ref failed, ok, $"退化三角形濾除（寫出 {written}）");
+            Report(ref failed, ok, $"degenerate triangle filtered ({written} written)");
         }
 
-        // 4)（可選）真實 STEP：B-rep 精細重新三角化 → 寫 binary STL 驗證
-        //（不測「較粗」：CADability GetTriangulation 對比快取粗的精度回傳既有快取，粗化無效 → 功能已移除）
+        // Optional real STEP input: retessellate B-rep geometry at fine precision.
         if (stepPath is not null)
         {
             var data = new StepImportService().Import(stepPath);
             var geos = Collect(data.Root).ToList();
             int importTris = data.Root.TriangleCount;
-            Console.WriteLine($"  來源 {IOPath.GetFileName(stepPath)}：{geos.Count} 個 B-rep 物件、匯入網格 {importTris:N0} 三角形");
+            Console.WriteLine($"  Source {IOPath.GetFileName(stepPath)}: {geos.Count} B-rep objects, {importTris:N0} imported triangles");
 
             var meshes = StlExportService.Tessellate(
                 geos, StlExportService.PrecisionFactor(StlMeshQuality.Fine));
@@ -82,13 +79,13 @@ public static class StlExportTest
             int written = StlExportService.Write(f, meshes, ascii: false, scale: 1.0);
             (uint count, _, _) = ReadBinary(f);
             Report(ref failed, meshes.Count > 0 && written > 0 && count == written,
-                $"精細重新三角化 {meshes.Count} 面 → {written:N0} 三角形");
-            // CADability 三角形數對精度非單調（0.4× 反而比 1× 少），Fine=0.15× 實測明顯更細
+                $"fine retessellation: {meshes.Count} faces, {written:N0} triangles");
+            // CADability's triangle count is not monotonic in precision; 0.15x is measurably finer.
             Report(ref failed, written > importTris,
-                $"精細（{written:N0}）> 匯入預設（{importTris:N0}）");
+                $"fine ({written:N0}) > imported default ({importTris:N0})");
         }
 
-        Console.WriteLine(failed == 0 ? "StlExportTest: PASS" : $"StlExportTest: FAIL（{failed} 項）");
+        Console.WriteLine(failed == 0 ? "StlExportTest: PASS" : $"StlExportTest: FAIL ({failed} checks)");
         return failed;
     }
 
@@ -106,7 +103,7 @@ public static class StlExportTest
         if (!ok) failed++;
     }
 
-    /// <summary>0..size 的軸對齊立方體，12 個三角形（法向不講究，STL 寫出時自算）</summary>
+    /// <summary>Axis-aligned cube from 0 to size, with 12 triangles.</summary>
     private static MeshGeometry3D BuildCube(double s)
     {
         var m = new MeshGeometry3D();
@@ -131,7 +128,7 @@ public static class StlExportTest
         using var br = new BinaryReader(File.OpenRead(path));
         byte[] header = br.ReadBytes(80);
         if (Encoding.ASCII.GetString(header, 0, 5) == "solid")
-            throw new InvalidDataException("binary STL header 不可以 solid 開頭");
+            throw new InvalidDataException("Binary STL header must not begin with solid");
         uint count = br.ReadUInt32();
         float min = float.MaxValue, max = float.MinValue;
         for (uint t = 0; t < count; t++)
diff --git a/tools/SmokeTest/TreeDump.cs b/tools/SmokeTest/TreeDump.cs
index af7ae9a..c27bde7 100644
--- a/tools/SmokeTest/TreeDump.cs
+++ b/tools/SmokeTest/TreeDump.cs
@@ -1,4 +1,4 @@
-// 實驗工具：印出 STEP 匯入後的物件階層（HierarchyToBlocks=true）
+// Print the STEP object hierarchy after import with HierarchyToBlocks enabled.
 using CADability;
 using CADability.GeoObject;