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/settings.py

@@ -17,10 +17,16 @@ from utils.levels import (
 router = Router()
 
 
+def get_translation_language(user) -> str:
+    """Получить язык перевода (translation_language или language_interface как fallback)"""
+    return getattr(user, 'translation_language', None) or getattr(user, 'language_interface', 'ru') or 'ru'
+
+
 def get_settings_keyboard(user) -> InlineKeyboardMarkup:
     """Создать клавиатуру настроек"""
     lang = get_user_lang(user)
     ui_lang_code = getattr(user, 'language_interface', 'ru') or 'ru'
+    translation_lang_code = get_translation_language(user)
     current_level = get_user_level_for_language(user)
     keyboard = InlineKeyboardMarkup(inline_keyboard=[
         [InlineKeyboardButton(
@@ -35,6 +41,10 @@ def get_settings_keyboard(user) -> InlineKeyboardMarkup:
             text=t(lang, 'settings.interface_prefix') + t(lang, f'settings.lang_name.{ui_lang_code}'),
             callback_data="settings_language"
         )],
+        [InlineKeyboardButton(
+            text=t(lang, 'settings.translation_prefix') + t(lang, f'settings.lang_name.{translation_lang_code}'),
+            callback_data="settings_translation"
+        )],
         [InlineKeyboardButton(
             text=t(lang, 'settings.close'),
             callback_data="settings_close"
@@ -73,6 +83,18 @@ def get_language_keyboard(user=None) -> InlineKeyboardMarkup:
     return keyboard
 
 
+def get_translation_language_keyboard(user=None) -> InlineKeyboardMarkup:
+    """Клавиатура выбора языка перевода"""
+    lang = get_user_lang(user)
+    keyboard = InlineKeyboardMarkup(inline_keyboard=[
+        [InlineKeyboardButton(text=t(lang, 'settings.lang_name.ru'), callback_data="set_translation_ru")],
+        [InlineKeyboardButton(text=t(lang, 'settings.lang_name.en'), callback_data="set_translation_en")],
+        [InlineKeyboardButton(text=t(lang, 'settings.lang_name.ja'), callback_data="set_translation_ja")],
+        [InlineKeyboardButton(text=t(lang, 'settings.back'), callback_data="settings_back")]
+    ])
+    return keyboard
+
+
 def get_learning_language_keyboard(user=None) -> InlineKeyboardMarkup:
     """Клавиатура выбора языка изучения"""
     lang = get_user_lang(user)
@@ -214,6 +236,40 @@ async def set_language(callback: CallbackQuery):
     await callback.answer()
 
 
+@router.callback_query(F.data == "settings_translation")
+async def settings_translation(callback: CallbackQuery):
+    """Показать выбор языка перевода"""
+    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)
+    await callback.message.edit_text(
+        t(lang, 'settings.translation_title') + t(lang, 'settings.translation_desc'),
+        reply_markup=get_translation_language_keyboard(user)
+    )
+    await callback.answer()
+
+
+@router.callback_query(F.data.startswith("set_translation_"))
+async def set_translation_language(callback: CallbackQuery):
+    """Установить язык перевода"""
+    new_translation_lang = callback.data.split("_")[-1]  # ru | en | ja
+
+    async with async_session_maker() as session:
+        user = await UserService.get_user_by_telegram_id(session, callback.from_user.id)
+
+        if user:
+            await UserService.update_user_translation_language(session, user.id, new_translation_lang)
+            lang = get_user_lang(user)
+            lang_name = t(lang, f'settings.lang_name.{new_translation_lang}')
+            text = t(lang, 'settings.translation_changed', lang_name=lang_name)
+            await callback.message.edit_text(
+                text,
+                reply_markup=InlineKeyboardMarkup(inline_keyboard=[[InlineKeyboardButton(text=t(lang, 'settings.back'), callback_data="settings_back")]])
+            )
+
+    await callback.answer()
+
+
 @router.callback_query(F.data == "settings_back")
 async def settings_back(callback: CallbackQuery):
     """Вернуться к настройкам"""