Add [localization]: add i18n middleware

src/bot/middlewares/i18n.py

@@ -0,0 +1,38 @@
+__all__ = ["I18nMiddleware"]
+
+
+from typing import Any, Dict
+
+from aiogram.types import TelegramObject
+from aiogram.utils.i18n import SimpleI18nMiddleware
+
+from database.models import TelegramUser
+
+
+class I18nMiddleware(SimpleI18nMiddleware):
+    """
+    Middleware for providing the user's language code.
+    Used for localizing bot messages.
+    """
+
+    async def get_locale(
+        self,
+        event: TelegramObject,
+        data: Dict[str, Any],
+    ) -> str:
+        """
+        Retrieving the user's language code.
+
+        Args:
+            event (TelegramObject): The incoming event.
+            data (Dict[str, Any]): Data for the event.
+
+        Returns:
+            str: user's language code.
+        """
+        telegram_user: TelegramUser | None = data.get("telegram_user")
+
+        if telegram_user is None:
+            return self.i18n.default_locale
+
+        return telegram_user.lang