feat(i18n): add English + Chinese localization

The app had zero localization ("软件多语言做了吗" — no). Add Flutter's
official gen-l10n pipeline and localize the core flow the user sees.

- pubspec: flutter_localizations + intl + generate: true
- l10n.yaml + lib/l10n/app_en.arb + app_zh.arb (37 strings)
- main.dart: localizationsDelegates + supportedLocales (follows OS locale)
- pen editor: all tool tooltips, page pill, error states localized
- home: app bar actions + empty-state buttons localized

Proven end-to-end: l10n_test pumps the same widget under Locale('en')
and Locale('zh') and asserts English vs Chinese strings resolve.

flutter analyze: 0 issues. l10n_test: 3/3 pass.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

lib/editor/canvas/pen_editor_screen.dart

@@ -8,6 +8,7 @@
 import 'package:flutter/material.dart';
 import 'package:pdfrx/pdfrx.dart';
 
+import '../../l10n/app_localizations.dart';
 import '../../services/database_service.dart';
 import '../engine/stroke_geometry.dart' show kDefaultPenThinning;
 import '../engine/stroke_model.dart';
@@ -398,6 +399,7 @@ class _PenEditorScreenState extends State<PenEditorScreen> {
 
   @override
   Widget build(BuildContext context) {
+    final l = AppLocalizations.of(context);
     return Scaffold(
       body: Stack(
         children: [
@@ -429,7 +431,7 @@ class _PenEditorScreenState extends State<PenEditorScreen> {
               padding: const EdgeInsets.all(8),
               child: _RoundIconButton(
                 icon: Icons.arrow_back,
-                tooltip: 'Back',
+                tooltip: l.back,
                 onPressed: () => Navigator.of(context).maybePop(),
               ),
             ),
@@ -510,15 +512,16 @@ class _PenEditorScreenState extends State<PenEditorScreen> {
   }
 
   Widget _buildBody() {
+    final l = AppLocalizations.of(context);
     if (_openError != null) {
-      return Center(child: Text('Failed to open PDF:\n$_openError'));
+      return Center(child: Text(l.failedToOpenPdf('$_openError')));
     }
     final doc = _document;
     if (doc == null) {
       return const Center(child: CircularProgressIndicator());
     }
     if (doc.pages.isEmpty) {
-      return const Center(child: Text('PDF has no pages.'));
+      return Center(child: Text(l.pdfNoPages));
     }
 
     final page = doc.pages[_pageIndex];
@@ -584,6 +587,7 @@ class _PenEditorScreenState extends State<PenEditorScreen> {
   /// tools, color dots, and finger-drawing toggle.
   Widget _buildToolPalette() {
     final cs = Theme.of(context).colorScheme;
+    final l = AppLocalizations.of(context);
     return Material(
       color: cs.surfaceContainerHigh,
       elevation: 3,
@@ -596,19 +600,19 @@ class _PenEditorScreenState extends State<PenEditorScreen> {
             _ToolButton(
               icon: Icons.edit_outlined,
               selected: _tool == CanvasTool.pen,
-              tooltip: 'Pen',
+              tooltip: l.toolPen,
               onPressed: () => setState(() => _tool = CanvasTool.pen),
             ),
             _ToolButton(
               icon: Icons.brush_outlined,
               selected: _tool == CanvasTool.highlighter,
-              tooltip: 'Highlighter',
+              tooltip: l.toolHighlighter,
               onPressed: () => setState(() => _tool = CanvasTool.highlighter),
             ),
             _ToolButton(
               icon: Icons.cleaning_services_outlined,
               selected: _tool == CanvasTool.eraser,
-              tooltip: 'Eraser',
+              tooltip: l.toolEraser,
               onPressed: () => setState(() => _tool = CanvasTool.eraser),
             ),
             _Divider(cs: cs),
@@ -616,13 +620,13 @@ class _PenEditorScreenState extends State<PenEditorScreen> {
             _ToolButton(
               icon: Icons.undo,
               selected: false,
-              tooltip: 'Undo',
+              tooltip: l.actionUndo,
               onPressed: _undoFor(_pageIndex).canUndo ? _performUndo : null,
             ),
             _ToolButton(
               icon: Icons.redo,
               selected: false,
-              tooltip: 'Redo',
+              tooltip: l.actionRedo,
               onPressed: _undoFor(_pageIndex).canRedo ? _performRedo : null,
             ),
             _Divider(cs: cs),
@@ -632,28 +636,28 @@ class _PenEditorScreenState extends State<PenEditorScreen> {
               icon: _allowFingerDrawing ? Icons.touch_app : Icons.do_not_touch,
               selected: _allowFingerDrawing,
               tooltip: _allowFingerDrawing
-                  ? 'Finger drawing ON'
-                  : 'Finger drawing OFF (pen only)',
+                  ? l.fingerDrawingOn
+                  : l.fingerDrawingOff,
               onPressed: _toggleFingerDrawing,
             ),
             // Page thumbnail grid.
             _ToolButton(
               icon: Icons.grid_view,
               selected: false,
-              tooltip: 'Pages',
+              tooltip: l.pages,
               onPressed: _document != null ? _openThumbnails : null,
             ),
             // Pen settings.
             _ToolButton(
               icon: Icons.settings_outlined,
               selected: false,
-              tooltip: 'Pen settings',
+              tooltip: l.penSettings,
               onPressed: _penConfig != null ? _openPenSettings : null,
             ),
             _ToolButton(
               icon: Icons.bug_report_outlined,
               selected: _showPenDebug,
-              tooltip: 'Input diagnostic (writes a log file)',
+              tooltip: l.inputDiagnostic,
               onPressed: () {
                 final on = !_showPenDebug;
                 setState(() => _showPenDebug = on);
@@ -699,6 +703,7 @@ class _PenEditorScreenState extends State<PenEditorScreen> {
   Widget _buildPagePill() {
     final doc = _document!;
     final cs = Theme.of(context).colorScheme;
+    final l = AppLocalizations.of(context);
     final total = doc.pages.length;
     final shown = (_scrub ?? (_pageIndex + 1).toDouble()).round();
     return Column(
@@ -742,7 +747,7 @@ class _PenEditorScreenState extends State<PenEditorScreen> {
               mainAxisSize: MainAxisSize.min,
               children: [
                 IconButton(
-                  tooltip: 'Previous page',
+                  tooltip: l.previousPage,
                   icon: const Icon(Icons.chevron_left),
                   onPressed:
                       _pageIndex > 0 ? () => _goToPage(_pageIndex - 1) : null,
@@ -752,7 +757,7 @@ class _PenEditorScreenState extends State<PenEditorScreen> {
                       ? () => setState(() => _showSlider = !_showSlider)
                       : null,
                   child: Text(
-                    '$shown / $total',
+                    l.pageOfPages(shown, total),
                     style: TextStyle(
                       color: cs.onSurface,
                       fontWeight: FontWeight.w600,
@@ -760,7 +765,7 @@ class _PenEditorScreenState extends State<PenEditorScreen> {
                   ),
                 ),
                 IconButton(
-                  tooltip: 'Next page',
+                  tooltip: l.nextPage,
                   icon: const Icon(Icons.chevron_right),
                   onPressed: _pageIndex < total - 1
                       ? () => _goToPage(_pageIndex + 1)

lib/l10n/app_en.arb

@@ -0,0 +1,46 @@
+{
+  "@@locale": "en",
+  "appTitle": "BadNote",
+  "settings": "Settings",
+  "search": "Search",
+  "importPdf": "Import PDF",
+  "importPpt": "Import PPT",
+  "penCanvasBeta": "Pen Canvas (beta)",
+  "newNote": "New Note",
+  "open": "Open",
+  "cancel": "Cancel",
+  "delete": "Delete",
+  "deleteNoteTitle": "Delete note?",
+  "deleteNote": "Delete note",
+  "openInSplitView": "Open in Split View",
+  "splitViewSubtitle": "PDF reference + scratchpad",
+  "removeDocument": "Remove document",
+  "processingPptx": "Processing PPTX...",
+  "processingPresentation": "Processing presentation...",
+  "couldNotOpenPresentation": "Could not open presentation.",
+  "toolPen": "Pen",
+  "toolHighlighter": "Highlighter",
+  "toolEraser": "Eraser",
+  "actionUndo": "Undo",
+  "actionRedo": "Redo",
+  "fingerDrawingOn": "Finger drawing ON",
+  "fingerDrawingOff": "Finger drawing OFF (pen only)",
+  "pages": "Pages",
+  "penSettings": "Pen settings",
+  "inputDiagnostic": "Input diagnostic (writes a log file)",
+  "back": "Back",
+  "previousPage": "Previous page",
+  "nextPage": "Next page",
+  "failedToOpenPdf": "Failed to open PDF:\n{error}",
+  "@failedToOpenPdf": {
+    "placeholders": { "error": { "type": "String" } }
+  },
+  "pdfNoPages": "PDF has no pages.",
+  "pageOfPages": "{current} / {total}",
+  "@pageOfPages": {
+    "placeholders": {
+      "current": { "type": "int" },
+      "total": { "type": "int" }
+    }
+  }
+}

lib/l10n/app_localizations.dart

@@ -0,0 +1,338 @@
+import 'dart:async';
+
+import 'package:flutter/foundation.dart';
+import 'package:flutter/widgets.dart';
+import 'package:flutter_localizations/flutter_localizations.dart';
+import 'package:intl/intl.dart' as intl;
+
+import 'app_localizations_en.dart';
+import 'app_localizations_zh.dart';
+
+// ignore_for_file: type=lint
+
+/// Callers can lookup localized strings with an instance of AppLocalizations
+/// returned by `AppLocalizations.of(context)`.
+///
+/// Applications need to include `AppLocalizations.delegate()` in their app's
+/// `localizationDelegates` list, and the locales they support in the app's
+/// `supportedLocales` list. For example:
+///
+/// ```dart
+/// import 'l10n/app_localizations.dart';
+///
+/// return MaterialApp(
+///   localizationsDelegates: AppLocalizations.localizationsDelegates,
+///   supportedLocales: AppLocalizations.supportedLocales,
+///   home: MyApplicationHome(),
+/// );
+/// ```
+///
+/// ## Update pubspec.yaml
+///
+/// Please make sure to update your pubspec.yaml to include the following
+/// packages:
+///
+/// ```yaml
+/// dependencies:
+///   # Internationalization support.
+///   flutter_localizations:
+///     sdk: flutter
+///   intl: any # Use the pinned version from flutter_localizations
+///
+///   # Rest of dependencies
+/// ```
+///
+/// ## iOS Applications
+///
+/// iOS applications define key application metadata, including supported
+/// locales, in an Info.plist file that is built into the application bundle.
+/// To configure the locales supported by your app, you’ll need to edit this
+/// file.
+///
+/// First, open your project’s ios/Runner.xcworkspace Xcode workspace file.
+/// Then, in the Project Navigator, open the Info.plist file under the Runner
+/// project’s Runner folder.
+///
+/// Next, select the Information Property List item, select Add Item from the
+/// Editor menu, then select Localizations from the pop-up menu.
+///
+/// Select and expand the newly-created Localizations item then, for each
+/// locale your application supports, add a new item and select the locale
+/// you wish to add from the pop-up menu in the Value field. This list should
+/// be consistent with the languages listed in the AppLocalizations.supportedLocales
+/// property.
+abstract class AppLocalizations {
+  AppLocalizations(String locale)
+    : localeName = intl.Intl.canonicalizedLocale(locale.toString());
+
+  final String localeName;
+
+  static AppLocalizations of(BuildContext context) {
+    return Localizations.of<AppLocalizations>(context, AppLocalizations)!;
+  }
+
+  static const LocalizationsDelegate<AppLocalizations> delegate =
+      _AppLocalizationsDelegate();
+
+  /// A list of this localizations delegate along with the default localizations
+  /// delegates.
+  ///
+  /// Returns a list of localizations delegates containing this delegate along with
+  /// GlobalMaterialLocalizations.delegate, GlobalCupertinoLocalizations.delegate,
+  /// and GlobalWidgetsLocalizations.delegate.
+  ///
+  /// Additional delegates can be added by appending to this list in
+  /// MaterialApp. This list does not have to be used at all if a custom list
+  /// of delegates is preferred or required.
+  static const List<LocalizationsDelegate<dynamic>> localizationsDelegates =
+      <LocalizationsDelegate<dynamic>>[
+        delegate,
+        GlobalMaterialLocalizations.delegate,
+        GlobalCupertinoLocalizations.delegate,
+        GlobalWidgetsLocalizations.delegate,
+      ];
+
+  /// A list of this localizations delegate's supported locales.
+  static const List<Locale> supportedLocales = <Locale>[
+    Locale('en'),
+    Locale('zh'),
+  ];
+
+  /// No description provided for @appTitle.
+  ///
+  /// In en, this message translates to:
+  /// **'BadNote'**
+  String get appTitle;
+
+  /// No description provided for @settings.
+  ///
+  /// In en, this message translates to:
+  /// **'Settings'**
+  String get settings;
+
+  /// No description provided for @search.
+  ///
+  /// In en, this message translates to:
+  /// **'Search'**
+  String get search;
+
+  /// No description provided for @importPdf.
+  ///
+  /// In en, this message translates to:
+  /// **'Import PDF'**
+  String get importPdf;
+
+  /// No description provided for @importPpt.
+  ///
+  /// In en, this message translates to:
+  /// **'Import PPT'**
+  String get importPpt;
+
+  /// No description provided for @penCanvasBeta.
+  ///
+  /// In en, this message translates to:
+  /// **'Pen Canvas (beta)'**
+  String get penCanvasBeta;
+
+  /// No description provided for @newNote.
+  ///
+  /// In en, this message translates to:
+  /// **'New Note'**
+  String get newNote;
+
+  /// No description provided for @open.
+  ///
+  /// In en, this message translates to:
+  /// **'Open'**
+  String get open;
+
+  /// No description provided for @cancel.
+  ///
+  /// In en, this message translates to:
+  /// **'Cancel'**
+  String get cancel;
+
+  /// No description provided for @delete.
+  ///
+  /// In en, this message translates to:
+  /// **'Delete'**
+  String get delete;
+
+  /// No description provided for @deleteNoteTitle.
+  ///
+  /// In en, this message translates to:
+  /// **'Delete note?'**
+  String get deleteNoteTitle;
+
+  /// No description provided for @deleteNote.
+  ///
+  /// In en, this message translates to:
+  /// **'Delete note'**
+  String get deleteNote;
+
+  /// No description provided for @openInSplitView.
+  ///
+  /// In en, this message translates to:
+  /// **'Open in Split View'**
+  String get openInSplitView;
+
+  /// No description provided for @splitViewSubtitle.
+  ///
+  /// In en, this message translates to:
+  /// **'PDF reference + scratchpad'**
+  String get splitViewSubtitle;
+
+  /// No description provided for @removeDocument.
+  ///
+  /// In en, this message translates to:
+  /// **'Remove document'**
+  String get removeDocument;
+
+  /// No description provided for @processingPptx.
+  ///
+  /// In en, this message translates to:
+  /// **'Processing PPTX...'**
+  String get processingPptx;
+
+  /// No description provided for @processingPresentation.
+  ///
+  /// In en, this message translates to:
+  /// **'Processing presentation...'**
+  String get processingPresentation;
+
+  /// No description provided for @couldNotOpenPresentation.
+  ///
+  /// In en, this message translates to:
+  /// **'Could not open presentation.'**
+  String get couldNotOpenPresentation;
+
+  /// No description provided for @toolPen.
+  ///
+  /// In en, this message translates to:
+  /// **'Pen'**
+  String get toolPen;
+
+  /// No description provided for @toolHighlighter.
+  ///
+  /// In en, this message translates to:
+  /// **'Highlighter'**
+  String get toolHighlighter;
+
+  /// No description provided for @toolEraser.
+  ///
+  /// In en, this message translates to:
+  /// **'Eraser'**
+  String get toolEraser;
+
+  /// No description provided for @actionUndo.
+  ///
+  /// In en, this message translates to:
+  /// **'Undo'**
+  String get actionUndo;
+
+  /// No description provided for @actionRedo.
+  ///
+  /// In en, this message translates to:
+  /// **'Redo'**
+  String get actionRedo;
+
+  /// No description provided for @fingerDrawingOn.
+  ///
+  /// In en, this message translates to:
+  /// **'Finger drawing ON'**
+  String get fingerDrawingOn;
+
+  /// No description provided for @fingerDrawingOff.
+  ///
+  /// In en, this message translates to:
+  /// **'Finger drawing OFF (pen only)'**
+  String get fingerDrawingOff;
+
+  /// No description provided for @pages.
+  ///
+  /// In en, this message translates to:
+  /// **'Pages'**
+  String get pages;
+
+  /// No description provided for @penSettings.
+  ///
+  /// In en, this message translates to:
+  /// **'Pen settings'**
+  String get penSettings;
+
+  /// No description provided for @inputDiagnostic.
+  ///
+  /// In en, this message translates to:
+  /// **'Input diagnostic (writes a log file)'**
+  String get inputDiagnostic;
+
+  /// No description provided for @back.
+  ///
+  /// In en, this message translates to:
+  /// **'Back'**
+  String get back;
+
+  /// No description provided for @previousPage.
+  ///
+  /// In en, this message translates to:
+  /// **'Previous page'**
+  String get previousPage;
+
+  /// No description provided for @nextPage.
+  ///
+  /// In en, this message translates to:
+  /// **'Next page'**
+  String get nextPage;
+
+  /// No description provided for @failedToOpenPdf.
+  ///
+  /// In en, this message translates to:
+  /// **'Failed to open PDF:\n{error}'**
+  String failedToOpenPdf(String error);
+
+  /// No description provided for @pdfNoPages.
+  ///
+  /// In en, this message translates to:
+  /// **'PDF has no pages.'**
+  String get pdfNoPages;
+
+  /// No description provided for @pageOfPages.
+  ///
+  /// In en, this message translates to:
+  /// **'{current} / {total}'**
+  String pageOfPages(int current, int total);
+}
+
+class _AppLocalizationsDelegate
+    extends LocalizationsDelegate<AppLocalizations> {
+  const _AppLocalizationsDelegate();
+
+  @override
+  Future<AppLocalizations> load(Locale locale) {
+    return SynchronousFuture<AppLocalizations>(lookupAppLocalizations(locale));
+  }
+
+  @override
+  bool isSupported(Locale locale) =>
+      <String>['en', 'zh'].contains(locale.languageCode);
+
+  @override
+  bool shouldReload(_AppLocalizationsDelegate old) => false;
+}
+
+AppLocalizations lookupAppLocalizations(Locale locale) {
+  // Lookup logic when only language code is specified.
+  switch (locale.languageCode) {
+    case 'en':
+      return AppLocalizationsEn();
+    case 'zh':
+      return AppLocalizationsZh();
+  }
+
+  throw FlutterError(
+    'AppLocalizations.delegate failed to load unsupported locale "$locale". This is likely '
+    'an issue with the localizations generation tool. Please file an issue '
+    'on GitHub with a reproducible sample app and the gen-l10n configuration '
+    'that was used.',
+  );
+}

lib/l10n/app_localizations_en.dart

@@ -0,0 +1,116 @@
+// ignore: unused_import
+import 'package:intl/intl.dart' as intl;
+import 'app_localizations.dart';
+
+// ignore_for_file: type=lint
+
+/// The translations for English (`en`).
+class AppLocalizationsEn extends AppLocalizations {
+  AppLocalizationsEn([String locale = 'en']) : super(locale);
+
+  @override
+  String get appTitle => 'BadNote';
+
+  @override
+  String get settings => 'Settings';
+
+  @override
+  String get search => 'Search';
+
+  @override
+  String get importPdf => 'Import PDF';
+
+  @override
+  String get importPpt => 'Import PPT';
+
+  @override
+  String get penCanvasBeta => 'Pen Canvas (beta)';
+
+  @override
+  String get newNote => 'New Note';
+
+  @override
+  String get open => 'Open';
+
+  @override
+  String get cancel => 'Cancel';
+
+  @override
+  String get delete => 'Delete';
+
+  @override
+  String get deleteNoteTitle => 'Delete note?';
+
+  @override
+  String get deleteNote => 'Delete note';
+
+  @override
+  String get openInSplitView => 'Open in Split View';
+
+  @override
+  String get splitViewSubtitle => 'PDF reference + scratchpad';
+
+  @override
+  String get removeDocument => 'Remove document';
+
+  @override
+  String get processingPptx => 'Processing PPTX...';
+
+  @override
+  String get processingPresentation => 'Processing presentation...';
+
+  @override
+  String get couldNotOpenPresentation => 'Could not open presentation.';
+
+  @override
+  String get toolPen => 'Pen';
+
+  @override
+  String get toolHighlighter => 'Highlighter';
+
+  @override
+  String get toolEraser => 'Eraser';
+
+  @override
+  String get actionUndo => 'Undo';
+
+  @override
+  String get actionRedo => 'Redo';
+
+  @override
+  String get fingerDrawingOn => 'Finger drawing ON';
+
+  @override
+  String get fingerDrawingOff => 'Finger drawing OFF (pen only)';
+
+  @override
+  String get pages => 'Pages';
+
+  @override
+  String get penSettings => 'Pen settings';
+
+  @override
+  String get inputDiagnostic => 'Input diagnostic (writes a log file)';
+
+  @override
+  String get back => 'Back';
+
+  @override
+  String get previousPage => 'Previous page';
+
+  @override
+  String get nextPage => 'Next page';
+
+  @override
+  String failedToOpenPdf(String error) {
+    return 'Failed to open PDF:\n$error';
+  }
+
+  @override
+  String get pdfNoPages => 'PDF has no pages.';
+
+  @override
+  String pageOfPages(int current, int total) {
+    return '$current / $total';
+  }
+}

lib/l10n/app_localizations_zh.dart

@@ -0,0 +1,116 @@
+// ignore: unused_import
+import 'package:intl/intl.dart' as intl;
+import 'app_localizations.dart';
+
+// ignore_for_file: type=lint
+
+/// The translations for Chinese (`zh`).
+class AppLocalizationsZh extends AppLocalizations {
+  AppLocalizationsZh([String locale = 'zh']) : super(locale);
+
+  @override
+  String get appTitle => 'BadNote';
+
+  @override
+  String get settings => '设置';
+
+  @override
+  String get search => '搜索';
+
+  @override
+  String get importPdf => '导入 PDF';
+
+  @override
+  String get importPpt => '导入 PPT';
+
+  @override
+  String get penCanvasBeta => '手写画布（测试版）';
+
+  @override
+  String get newNote => '新建笔记';
+
+  @override
+  String get open => '打开';
+
+  @override
+  String get cancel => '取消';
+
+  @override
+  String get delete => '删除';
+
+  @override
+  String get deleteNoteTitle => '删除笔记？';
+
+  @override
+  String get deleteNote => '删除笔记';
+
+  @override
+  String get openInSplitView => '分屏打开';
+
+  @override
+  String get splitViewSubtitle => 'PDF 参考 + 草稿纸';
+
+  @override
+  String get removeDocument => '移除文档';
+
+  @override
+  String get processingPptx => '正在处理 PPTX…';
+
+  @override
+  String get processingPresentation => '正在处理演示文稿…';
+
+  @override
+  String get couldNotOpenPresentation => '无法打开演示文稿。';
+
+  @override
+  String get toolPen => '钢笔';
+
+  @override
+  String get toolHighlighter => '荧光笔';
+
+  @override
+  String get toolEraser => '橡皮擦';
+
+  @override
+  String get actionUndo => '撤销';
+
+  @override
+  String get actionRedo => '重做';
+
+  @override
+  String get fingerDrawingOn => '手指书写：开';
+
+  @override
+  String get fingerDrawingOff => '手指书写：关（仅手写笔）';
+
+  @override
+  String get pages => '页面';
+
+  @override
+  String get penSettings => '手写笔设置';
+
+  @override
+  String get inputDiagnostic => '输入诊断（写入日志文件）';
+
+  @override
+  String get back => '返回';
+
+  @override
+  String get previousPage => '上一页';
+
+  @override
+  String get nextPage => '下一页';
+
+  @override
+  String failedToOpenPdf(String error) {
+    return '打开 PDF 失败：\n$error';
+  }
+
+  @override
+  String get pdfNoPages => 'PDF 没有任何页面。';
+
+  @override
+  String pageOfPages(int current, int total) {
+    return '$current / $total';
+  }
+}

lib/l10n/app_zh.arb

@@ -0,0 +1,37 @@
+{
+  "@@locale": "zh",
+  "appTitle": "BadNote",
+  "settings": "设置",
+  "search": "搜索",
+  "importPdf": "导入 PDF",
+  "importPpt": "导入 PPT",
+  "penCanvasBeta": "手写画布（测试版）",
+  "newNote": "新建笔记",
+  "open": "打开",
+  "cancel": "取消",
+  "delete": "删除",
+  "deleteNoteTitle": "删除笔记？",
+  "deleteNote": "删除笔记",
+  "openInSplitView": "分屏打开",
+  "splitViewSubtitle": "PDF 参考 + 草稿纸",
+  "removeDocument": "移除文档",
+  "processingPptx": "正在处理 PPTX…",
+  "processingPresentation": "正在处理演示文稿…",
+  "couldNotOpenPresentation": "无法打开演示文稿。",
+  "toolPen": "钢笔",
+  "toolHighlighter": "荧光笔",
+  "toolEraser": "橡皮擦",
+  "actionUndo": "撤销",
+  "actionRedo": "重做",
+  "fingerDrawingOn": "手指书写：开",
+  "fingerDrawingOff": "手指书写：关（仅手写笔）",
+  "pages": "页面",
+  "penSettings": "手写笔设置",
+  "inputDiagnostic": "输入诊断（写入日志文件）",
+  "back": "返回",
+  "previousPage": "上一页",
+  "nextPage": "下一页",
+  "failedToOpenPdf": "打开 PDF 失败：\n{error}",
+  "pdfNoPages": "PDF 没有任何页面。",
+  "pageOfPages": "{current} / {total}"
+}

lib/main.dart

@@ -1,11 +1,13 @@
 import 'package:dynamic_color/dynamic_color.dart';
 import 'package:flutter/material.dart';
+import 'package:flutter_localizations/flutter_localizations.dart';
 import 'package:flutter_riverpod/flutter_riverpod.dart';
 import 'package:google_fonts/google_fonts.dart';
 import 'package:pdfrx/pdfrx.dart';
 import 'package:shared_preferences/shared_preferences.dart';
 
 import 'editor/pdf/pen_capture_region.dart';
+import 'l10n/app_localizations.dart';
 import 'providers/settings_provider.dart';
 import 'screens/home_screen.dart';
 import 'services/database_service.dart';
@@ -54,6 +56,14 @@ class BadNoteApp extends ConsumerWidget {
           themeMode: settings.themeMode,
           theme: _theme(lightScheme),
           darkTheme: _theme(darkScheme),
+          // i18n: follows the OS language (en / zh) via the system locale.
+          localizationsDelegates: const [
+            AppLocalizations.delegate,
+            GlobalMaterialLocalizations.delegate,
+            GlobalWidgetsLocalizations.delegate,
+            GlobalCupertinoLocalizations.delegate,
+          ],
+          supportedLocales: AppLocalizations.supportedLocales,
           home: const HomeScreen(),
         );
       },

lib/screens/home_screen.dart

@@ -1,5 +1,6 @@
 import 'package:flutter/material.dart';
 import 'package:flutter_riverpod/flutter_riverpod.dart';
+import '../l10n/app_localizations.dart';
 import '../models/document.dart';
 import '../models/note.dart';
 import '../providers/document_provider.dart';
@@ -34,15 +35,16 @@ class HomeScreen extends ConsumerWidget {
   @override
   Widget build(BuildContext context, WidgetRef ref) {
     final notesAsync = ref.watch(noteListProvider);
+    final l = AppLocalizations.of(context);
 
     return Scaffold(
       appBar: AppBar(
-        title: const Text('BadNote'),
+        title: Text(l.appTitle),
         centerTitle: true,
         actions: [
           IconButton(
             icon: const Icon(Icons.settings),
-            tooltip: 'Settings',
+            tooltip: l.settings,
             onPressed: () {
               Navigator.of(
                 context,
@@ -51,17 +53,17 @@ class HomeScreen extends ConsumerWidget {
           ),
           IconButton(
             icon: const Icon(Icons.picture_as_pdf),
-            tooltip: 'Import PDF',
+            tooltip: l.importPdf,
             onPressed: () => _importPdf(context),
           ),
           IconButton(
             icon: const Icon(Icons.slideshow),
-            tooltip: 'Import PPT',
+            tooltip: l.importPpt,
             onPressed: () => _importPptx(context),
           ),
           IconButton(
             icon: const Icon(Icons.search),
-            tooltip: 'Search',
+            tooltip: l.search,
             onPressed: () {
               Navigator.of(
                 context,
@@ -71,7 +73,7 @@ class HomeScreen extends ConsumerWidget {
           // New pen-first canvas editor (beta).
           IconButton(
             icon: const Icon(Icons.draw_outlined),
-            tooltip: 'Pen Canvas (beta)',
+            tooltip: l.penCanvasBeta,
             onPressed: () => openM1Spike(context),
           ),
         ],
@@ -265,19 +267,19 @@ class HomeScreen extends ConsumerWidget {
           FilledButton.icon(
             onPressed: () => _createAndOpenNote(context, ref),
             icon: const Icon(Icons.add),
-            label: const Text('New Note'),
+            label: Text(AppLocalizations.of(context).newNote),
           ),
           const SizedBox(height: 12),
           OutlinedButton.icon(
             onPressed: () => _importPdf(context),
             icon: const Icon(Icons.picture_as_pdf),
-            label: const Text('Import PDF'),
+            label: Text(AppLocalizations.of(context).importPdf),
           ),
           const SizedBox(height: 12),
           OutlinedButton.icon(
             onPressed: () => _importPptx(context),
             icon: const Icon(Icons.slideshow),
-            label: const Text('Import PPT'),
+            label: Text(AppLocalizations.of(context).importPpt),
           ),
         ],
       ),