refactor(i18n): share supported language choices

Use one non-generated language catalog in setup and appearance settings. Filter supported locale codes once and retain the resulting immutable picker list.

lib/constants/language_choices.dart

@@ -0,0 +1,33 @@
+import 'package:flutter/material.dart';
+import 'package:spotiflac_android/l10n/supported_locales.dart';
+
+/// Display choices shared by onboarding and appearance settings.
+const appLanguageChoices = [
+  ('system', 'System Default', Icons.phone_android),
+  ('en', 'English', Icons.language),
+  ('ar', 'العربية', Icons.language),
+  ('id', 'Bahasa Indonesia', Icons.language),
+  ('de', 'Deutsch', Icons.language),
+  ('es', 'Español', Icons.language),
+  ('es_ES', 'Español (España)', Icons.language),
+  ('fr', 'Français', Icons.language),
+  ('hi', 'हिन्दी', Icons.language),
+  ('it', 'Italiano', Icons.language),
+  ('ja', '日本語', Icons.language),
+  ('ko', '한국어', Icons.language),
+  ('nl', 'Nederlands', Icons.language),
+  ('pt', 'Português', Icons.language),
+  ('pt_PT', 'Português (Brasil)', Icons.language),
+  ('ru', 'Русский', Icons.language),
+  ('tr', 'Türkçe', Icons.language),
+  ('uk', 'Українська', Icons.language),
+  ('zh_CN', '简体中文', Icons.language),
+  ('zh_TW', '繁體中文', Icons.language),
+];
+
+final supportedLanguageChoices = List<(String, String, IconData)>.unmodifiable(
+  appLanguageChoices.where(
+    (choice) =>
+        choice.$1 == 'system' || filteredLocaleCodes.contains(choice.$1),
+  ),
+);

lib/screens/settings/appearance_settings_page.dart

@@ -1,7 +1,7 @@
 import 'package:flutter/material.dart';
 import 'package:flutter_riverpod/flutter_riverpod.dart';
 import 'package:spotiflac_android/l10n/l10n.dart';
-import 'package:spotiflac_android/l10n/supported_locales.dart';
+import 'package:spotiflac_android/constants/language_choices.dart';
 import 'package:spotiflac_android/providers/settings_provider.dart';
 import 'package:spotiflac_android/providers/theme_provider.dart';
 import 'package:spotiflac_android/utils/adaptive_layout.dart';
@@ -552,39 +552,8 @@ class _LanguageSelector extends StatelessWidget {
     required this.onChanged,
   });
 
-  static const _allLanguages = [
-    ('system', 'System Default', Icons.phone_android),
-    ('en', 'English', Icons.language),
-    ('ar', 'العربية', Icons.language),
-    ('id', 'Bahasa Indonesia', Icons.language),
-    ('de', 'Deutsch', Icons.language),
-    ('es', 'Español', Icons.language),
-    ('es_ES', 'Español (España)', Icons.language),
-    ('fr', 'Français', Icons.language),
-    ('hi', 'हिन्दी', Icons.language),
-    ('it', 'Italiano', Icons.language),
-    ('ja', '日本語', Icons.language),
-    ('ko', '한국어', Icons.language),
-    ('nl', 'Nederlands', Icons.language),
-    ('pt', 'Português', Icons.language),
-    ('pt_PT', 'Português (Brasil)', Icons.language),
-    ('ru', 'Русский', Icons.language),
-    ('tr', 'Türkçe', Icons.language),
-    ('uk', 'Українська', Icons.language),
-    ('zh_CN', '简体中文', Icons.language),
-    ('zh_TW', '繁體中文', Icons.language),
-  ];
-
-  /// Uses filteredLocaleCodes from supported_locales.dart (generated file).
-  List<(String, String, IconData)> get _languages {
-    return _allLanguages.where((lang) {
-      if (lang.$1 == 'system') return true;
-      return filteredLocaleCodes.contains(lang.$1);
-    }).toList();
-  }
-
   String _getLanguageName(String code) {
-    for (final lang in _allLanguages) {
+    for (final lang in appLanguageChoices) {
       if (lang.$1 == code) return lang.$2;
     }
     return code;
@@ -629,9 +598,9 @@ class _LanguageSelector extends StatelessWidget {
             Flexible(
               child: ListView.builder(
                 shrinkWrap: true,
-                itemCount: _languages.length,
+                itemCount: supportedLanguageChoices.length,
                 itemBuilder: (context, index) {
-                  final lang = _languages[index];
+                  final lang = supportedLanguageChoices[index];
                   final isSelected = currentLocale == lang.$1;
                   return ListTile(
                     leading: Icon(

lib/screens/setup_screen.dart

@@ -7,7 +7,7 @@ import 'package:go_router/go_router.dart';
 import 'package:device_info_plus/device_info_plus.dart';
 import 'package:spotiflac_android/providers/settings_provider.dart';
 import 'package:spotiflac_android/l10n/l10n.dart';
-import 'package:spotiflac_android/l10n/supported_locales.dart';
+import 'package:spotiflac_android/constants/language_choices.dart';
 import 'package:spotiflac_android/services/platform_bridge.dart';
 import 'package:spotiflac_android/utils/adaptive_layout.dart';
 import 'package:spotiflac_android/utils/file_access.dart';
@@ -710,43 +710,13 @@ class _SetupScreenState extends ConsumerState<SetupScreen> {
     );
   }
 
-  static const _allLanguages = [
-    ('system', 'System Default', Icons.phone_android),
-    ('en', 'English', Icons.language),
-    ('ar', 'العربية', Icons.language),
-    ('id', 'Bahasa Indonesia', Icons.language),
-    ('de', 'Deutsch', Icons.language),
-    ('es', 'Español', Icons.language),
-    ('es_ES', 'Español (España)', Icons.language),
-    ('fr', 'Français', Icons.language),
-    ('hi', 'हिन्दी', Icons.language),
-    ('it', 'Italiano', Icons.language),
-    ('ja', '日本語', Icons.language),
-    ('ko', '한국어', Icons.language),
-    ('nl', 'Nederlands', Icons.language),
-    ('pt', 'Português', Icons.language),
-    ('pt_PT', 'Português (Brasil)', Icons.language),
-    ('ru', 'Русский', Icons.language),
-    ('tr', 'Türkçe', Icons.language),
-    ('uk', 'Українська', Icons.language),
-    ('zh_CN', '简体中文', Icons.language),
-    ('zh_TW', '繁體中文', Icons.language),
-  ];
-
-  List<(String, String, IconData)> get _filteredLanguages {
-    return _allLanguages.where((lang) {
-      if (lang.$1 == 'system') return true;
-      return filteredLocaleCodes.contains(lang.$1);
-    }).toList();
-  }
-
   void _onLanguageSelected(String locale) {
     setState(() => _selectedLocale = locale);
     ref.read(settingsProvider.notifier).setLocale(locale);
   }
 
   Widget _buildLanguageStep(ColorScheme colorScheme) {
-    final languages = _filteredLanguages;
+    final languages = supportedLanguageChoices;
 
     return LayoutBuilder(
       builder: (context, constraints) {