feat: add translation language setting & onboarding flow

- Add separate translation_language setting (independent from interface language)
- Implement 3-step onboarding for new users:
  1. Choose interface language
  2. Choose learning language
  3. Choose translation language
- Fix localization issues when using callback.message (user_id from state)
- Add UserService.get_user_by_id() method
- Add get_user_translation_lang() helper in i18n
- Update all handlers to use correct translation language
- Add localization keys for onboarding (ru/en/ja)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

bot/handlers/import_text.py

@@ -10,7 +10,7 @@ from database.models import WordSource
 from services.user_service import UserService
 from services.vocabulary_service import VocabularyService
 from services.ai_service import ai_service
-from utils.i18n import t, get_user_lang
+from utils.i18n import t, get_user_lang, get_user_translation_lang
 from utils.levels import get_user_level_for_language
 
 router = Router()
@@ -87,7 +87,7 @@ async def process_text(message: Message, state: FSMContext):
             level=current_level,
             max_words=15,
             learning_lang=user.learning_language,
-            translation_lang=user.language_interface,
+            translation_lang=get_user_translation_lang(user),
         )
 
         await processing_msg.delete()
@@ -176,27 +176,29 @@ async def import_single_word(callback: CallbackQuery, state: FSMContext):
     user_id = data.get('user_id')
 
     if word_index >= len(words):
-        await callback.answer("❌ Ошибка: слово не найдено")
+        await callback.answer(t('ru', 'words.err_not_found'))
         return
 
     word_data = words[word_index]
 
     async with async_session_maker() as session:
         user = await UserService.get_user_by_telegram_id(session, callback.from_user.id)
+        lang = get_user_lang(user)
+
         # Проверяем, нет ли уже такого слова
         existing = await VocabularyService.get_word_by_original(
             session, user_id, word_data['word']
         )
 
         if existing:
-            await callback.answer(f"Слово '{word_data['word']}' уже в словаре", show_alert=True)
+            await callback.answer(t(lang, 'words.already_exists', word=word_data['word']), show_alert=True)
             return
 
         # Добавляем слово
         learn = user.learning_language if user else 'en'
-        ui = user.language_interface if user else 'ru'
+        translation_lang = get_user_translation_lang(user)
         ctx = word_data.get('context')
-        examples = ([{learn: ctx, ui: ''}] if ctx else [])
+        examples = ([{learn: ctx, translation_lang: ''}] if ctx else [])
 
         await VocabularyService.add_word(
             session=session,
@@ -204,7 +206,7 @@ async def import_single_word(callback: CallbackQuery, state: FSMContext):
             word_original=word_data['word'],
             word_translation=word_data['translation'],
             source_lang=user.learning_language if user else None,
-            translation_lang=user.language_interface if user else None,
+            translation_lang=translation_lang,
             transcription=word_data.get('transcription'),
             examples=examples,
             source=WordSource.CONTEXT,
@@ -242,9 +244,9 @@ async def import_all_words(callback: CallbackQuery, state: FSMContext):
 
             # Добавляем слово
             learn = user.learning_language if user else 'en'
-            ui = user.language_interface if user else 'ru'
+            translation_lang = get_user_translation_lang(user)
             ctx = word_data.get('context')
-            examples = ([{learn: ctx, ui: ''}] if ctx else [])
+            examples = ([{learn: ctx, translation_lang: ''}] if ctx else [])
 
             await VocabularyService.add_word(
                 session=session,
@@ -252,7 +254,7 @@ async def import_all_words(callback: CallbackQuery, state: FSMContext):
                 word_original=word_data['word'],
                 word_translation=word_data['translation'],
                 source_lang=user.learning_language if user else None,
-                translation_lang=user.language_interface if user else None,
+                translation_lang=translation_lang,
                 transcription=word_data.get('transcription'),
                 examples=examples,
                 source=WordSource.CONTEXT,
@@ -389,7 +391,7 @@ async def handle_file_import(message: Message, state: FSMContext, bot: Bot):
         translations = await ai_service.translate_words_batch(
             words=words_to_translate,
             source_lang=user.learning_language,
-            translation_lang=user.language_interface
+            translation_lang=get_user_translation_lang(user)
         )
 
         await processing_msg.delete()
@@ -490,7 +492,7 @@ async def import_file_all_words(callback: CallbackQuery, state: FSMContext):
                 word_original=word_data['word'],
                 word_translation=word_data.get('translation', ''),
                 source_lang=user.learning_language if user else None,
-                translation_lang=user.language_interface if user else None,
+                translation_lang=get_user_translation_lang(user),
                 transcription=word_data.get('transcription'),
                 source=WordSource.IMPORT
             )