fix: update translation model ID retrieval and improve file name extraction in translation service

lib/screens/channel_chat_screen.dart

@@ -1172,7 +1172,7 @@ class _ChannelChatScreenState extends State<ChannelChatScreen> {
     String? translationModelId;
     if (settings.translationEnabled) {
       final targetLanguageCode = translationService.resolvedTargetLanguageCode(
-        settings.languageOverride,
+        Localizations.localeOf(context).languageCode,
       );
       if (translationService.shouldTranslateOutgoing(
         text: text,

lib/screens/chat_screen.dart

@@ -650,7 +650,7 @@ class _ChatScreenState extends State<ChatScreen> {
     String? translationModelId;
     if (settings.translationEnabled) {
       final targetLanguageCode = translationService.resolvedTargetLanguageCode(
-        settings.languageOverride,
+        Localizations.localeOf(context).languageCode,
       );
       if (translationService.shouldTranslateOutgoing(
         text: text,

lib/services/translation_service.dart

@@ -326,7 +326,7 @@ class TranslationService extends ChangeNotifier {
     }
     final trackedStream = _trackDownloadProgress(response.stream);
     await _fileStore.writeModelBytes(
-      fileName: chunkPath.split('/').last,
+      fileName: chunkPath.split(RegExp(r'[/\\]')).last,
       chunks: trackedStream,
     );
   }