feat: add message translation support

- Introduced translation functionality in chat screen, allowing users to translate messages before sending.
- Added MessageTranslationButton to the input bar for enabling/disabling translation.
- Implemented translation service to handle incoming and outgoing text translations using llama models.
- Enhanced message storage to include original and translated text, language codes, and translation status.
- Created UI components for displaying translated messages and managing translation options.
- Added translation model management, including downloading and storing models locally.
- Updated app settings to manage translation preferences and model selections.

lib/screens/chat_screen.dart

@@ -16,16 +16,17 @@ import '../connector/meshcore_protocol.dart';
 import '../helpers/reaction_helper.dart';
 import '../widgets/message_status_icon.dart';
 import '../helpers/chat_scroll_controller.dart';
-import '../helpers/link_handler.dart';
 import '../helpers/path_helper.dart';
 import '../helpers/utf8_length_limiter.dart';
 import '../models/channel_message.dart';
 import '../models/contact.dart';
 import '../models/message.dart';
 import '../models/path_history.dart';
+import '../models/translation_support.dart';
 import '../services/app_settings_service.dart';
 import '../services/chat_text_scale_service.dart';
 import '../services/path_history_service.dart';
+import '../services/translation_service.dart';
 import '../widgets/chat_zoom_wrapper.dart';
 import '../widgets/elements_ui.dart';
 import 'channel_message_path_screen.dart';
@@ -35,8 +36,10 @@ import '../widgets/emoji_picker.dart';
 import '../widgets/gif_message.dart';
 import '../widgets/jump_to_bottom_button.dart';
 import '../widgets/gif_picker.dart';
+import '../widgets/message_translation_button.dart';
 import '../widgets/path_selection_dialog.dart';
 import '../widgets/radio_stats_entry.dart';
+import '../widgets/translated_message_content.dart';
 import '../utils/app_logger.dart';
 import '../l10n/l10n.dart';
 import 'telemetry_screen.dart';
@@ -495,6 +498,7 @@ class _ChatScreenState extends State<ChatScreen> {
   Widget _buildInputBar(MeshCoreConnector connector) {
     final maxBytes = maxContactMessageBytes();
     final colorScheme = Theme.of(context).colorScheme;
+    final settings = context.watch<AppSettingsService>().settings;
     return Container(
       padding: const EdgeInsets.all(8),
       decoration: BoxDecoration(
@@ -509,6 +513,12 @@ class _ChatScreenState extends State<ChatScreen> {
               onPressed: () => _showGifPicker(context),
               tooltip: context.l10n.chat_sendGif,
             ),
+            if (settings.translationEnabled)
+              MessageTranslationButton(
+                enabled: settings.composerTranslationEnabled,
+                languageCode: settings.translationTargetLanguageCode,
+                onPressed: _showTranslationOptions,
+              ),
             Expanded(
               child: ValueListenableBuilder<TextEditingValue>(
                 valueListenable: _textController,
@@ -606,7 +616,19 @@ class _ChatScreenState extends State<ChatScreen> {
     );
   }
 
-  void _sendMessage(MeshCoreConnector connector) {
+  Future<void> _showTranslationOptions() async {
+    final settingsService = context.read<AppSettingsService>();
+    final settings = settingsService.settings;
+    await showMessageTranslationSheet(
+      context: context,
+      enabled: settings.composerTranslationEnabled,
+      selectedLanguageCode: settings.translationTargetLanguageCode,
+      onEnabledChanged: settingsService.setComposerTranslationEnabled,
+      onLanguageSelected: settingsService.setTranslationTargetLanguageCode,
+    );
+  }
+
+  Future<void> _sendMessage(MeshCoreConnector connector) async {
     final text = _textController.text.trim();
     if (text.isEmpty) return;
 
@@ -620,17 +642,54 @@ class _ChatScreenState extends State<ChatScreen> {
     }
     _lastTextSendAt = now;
 
+    // Clear input synchronously to prevent double-send
+    _textController.clear();
+    _textFieldFocusNode.requestFocus();
+
+    final settings = context.read<AppSettingsService>().settings;
+    final translationService = context.read<TranslationService>();
+    var outgoingText = text;
+    String? originalText;
+    String? translatedLanguageCode;
+    String? translationModelId;
+    if (settings.translationEnabled) {
+      final targetLanguageCode = translationService.resolvedTargetLanguageCode(
+        settings.languageOverride,
+      );
+      if (translationService.shouldTranslateOutgoing(
+        text: text,
+        targetLanguageCode: targetLanguageCode,
+      )) {
+        final result = await translationService.translateOutgoingText(
+          text: text,
+          targetLanguageCode: targetLanguageCode,
+        );
+        if (!mounted) return;
+        if (result != null &&
+            result.status == MessageTranslationStatus.completed &&
+            result.translatedText.isNotEmpty) {
+          outgoingText = result.translatedText;
+          originalText = text;
+          translatedLanguageCode = result.targetLanguageCode;
+          translationModelId = result.modelId;
+        }
+      }
+    }
     final maxBytes = maxContactMessageBytes();
-    if (utf8.encode(text).length > maxBytes) {
+    if (utf8.encode(outgoingText).length > maxBytes) {
       ScaffoldMessenger.of(context).showSnackBar(
         SnackBar(content: Text(context.l10n.chat_messageTooLong(maxBytes))),
       );
       return;
     }
 
-    connector.sendMessage(_resolveContact(connector), text);
-    _textController.clear();
-    _textFieldFocusNode.requestFocus();
+    connector.sendMessage(
+      _resolveContact(connector),
+      outgoingText,
+      originalText: originalText,
+      translatedLanguageCode: translatedLanguageCode,
+      translationModelId: translationModelId,
+    );
   }
 
   void _showPathHistory(BuildContext context) {
@@ -1533,6 +1592,14 @@ class _MessageBubble extends StatelessWidget {
     if (isRoomServer && !isOutgoing) {
       messageText = message.text.substring(4.clamp(0, message.text.length));
     }
+    final translatedDisplayText =
+        message.translatedText != null &&
+            message.translatedText!.trim().isNotEmpty
+        ? message.translatedText!.trim()
+        : messageText;
+    final originalDisplayText = isOutgoing
+        ? message.originalText
+        : (translatedDisplayText != messageText ? messageText : null);
     return Padding(
       padding: const EdgeInsets.symmetric(vertical: 4),
       child: Column(
@@ -1662,13 +1729,17 @@ class _MessageBubble extends StatelessWidget {
                             crossAxisAlignment: CrossAxisAlignment.end,
                             children: [
                               Flexible(
-                                child: LinkHandler.buildLinkifyText(
-                                  context: context,
-                                  text: messageText,
+                                child: TranslatedMessageContent(
+                                  displayText: translatedDisplayText,
+                                  originalText: originalDisplayText,
                                   style: TextStyle(
                                     color: textColor,
                                     fontSize: bodyFontSize * textScale,
                                   ),
+                                  originalStyle: TextStyle(
+                                    color: textColor.withValues(alpha: 0.78),
+                                    fontSize: bodyFontSize * textScale,
+                                  ),
                                 ),
                               ),
                               if (!enableTracing && isOutgoing) ...[