fix(subtitles): remember search language

close #1002

lib/services/settings_service.dart

@@ -271,6 +271,7 @@ class SettingsService extends BaseSharedPreferencesService {
   static const sleepTimerDuration = IntPref('sleep_timer_duration', defaultValue: 30);
   static const audioSyncOffset = IntPref('audio_sync_offset');
   static const subtitleSyncOffset = IntPref('subtitle_sync_offset');
+  static const subtitleSearchLanguage = NullableStringPref('subtitle_search_language');
   static const volume = DoublePref('volume', defaultValue: 100.0);
   static const rotationLocked = BoolPref('rotation_locked', defaultValue: true);
   static const subtitleFontSize = IntPref('subtitle_font_size', defaultValue: 38);
@@ -655,6 +656,7 @@ class SettingsService extends BaseSharedPreferencesService {
     sleepTimerDuration,
     audioSyncOffset,
     subtitleSyncOffset,
+    subtitleSearchLanguage,
     volume,
     maxVolume,
     subtitleFontSize,

lib/utils/language_codes.dart

@@ -25,6 +25,12 @@ class LanguageCodes {
     return variations.toList();
   }
 
+  static String? getIso6391Code(String code) {
+    final normalized = code.toLowerCase().trim().split(RegExp('[-_]')).first;
+    if (normalized.isEmpty) return null;
+    return _resolve(normalized)?.code1;
+  }
+
   /// Get a display name for a language/locale code.
   /// Handles plain codes ("en" → "English") and locale codes ("en-US" → "English",
   /// "en-AU" → "English (Australia)").

lib/widgets/video_controls/sheets/subtitle_search_sheet.dart

@@ -10,6 +10,7 @@ import '../../../i18n/strings.g.dart';
 import '../../../mixins/controller_disposer_mixin.dart';
 import '../../../models/plex/plex_subtitle_search_result.dart';
 import '../../../services/plex_client.dart';
+import '../../../services/settings_service.dart';
 import '../../../utils/language_codes.dart';
 import '../../../utils/provider_extensions.dart';
 import '../../../utils/snackbar_helper.dart';
@@ -20,6 +21,13 @@ import '../../../widgets/pill_input_decoration.dart';
 import 'base_video_control_sheet.dart';
 import '../../loading_indicator_box.dart';
 
+@visibleForTesting
+String resolveSubtitleSearchLanguageCode({String? savedLanguageCode, required Locale systemLocale}) {
+  return LanguageCodes.getIso6391Code(savedLanguageCode ?? '') ??
+      LanguageCodes.getIso6391Code(systemLocale.languageCode) ??
+      'en';
+}
+
 class SubtitleSearchSheet extends StatefulWidget {
   final String ratingKey;
   final String serverId;
@@ -62,13 +70,14 @@ class _SubtitleSearchSheetState extends State<SubtitleSearchSheet> with Controll
   }
 
   void _initDefaultLanguage() {
-    final locale = WidgetsBinding.instance.platformDispatcher.locale;
-    final code = locale.languageCode;
+    final code = resolveSubtitleSearchLanguageCode(
+      savedLanguageCode: SettingsService.instanceOrNull?.read(SettingsService.subtitleSearchLanguage),
+      systemLocale: WidgetsBinding.instance.platformDispatcher.locale,
+    );
     final name = LanguageCodes.getLanguageName(code);
-    if (name != null) {
-      _languageCode = code;
-      _languageName = name;
-    }
+    if (name == null) return;
+    _languageCode = code;
+    _languageName = name;
   }
 
   @override
@@ -153,6 +162,10 @@ class _SubtitleSearchSheetState extends State<SubtitleSearchSheet> with Controll
       _languageName = name;
       _showLanguagePicker = false;
     });
+    final settings = SettingsService.instanceOrNull;
+    if (settings != null) {
+      unawaited(settings.write(SettingsService.subtitleSearchLanguage, code));
+    }
     OverlaySheetController.of(context).refocus();
     _search();
   }