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CHANGES/1652.feature.rst

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+Feature: Example of dynamic language switching in aiogram bot using i18n utilities, allowing real-time translation.

examples/i18n.py

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+"""
+Original docs link: https://docs.aiogram.dev/en/dev-3.x/utils/i18n.html
+PROBLEM SOLUTION PROVIDED:
+Aiogram handlers remember language on the start and there's no chance of changing it in handler's runtime.
+So, here's a little hack in `change_language handler`
+
+# Cheatsheet to create/update locales:
+## Generating new:
+1. `pybabel extract -k __ --input-dirs=. -o locales/messages.pot`
+2. `pybabel init -i locales/messages.pot -d locales -D messages -l <en ru uk>`
+3. Open `locales/{language}/LC_MESSAGES/messages.po` and Translate msgs
+4. `pybabel compile -d locales -D messages`
+
+## Updating:
+1. `pybabel extract -k __ --input-dirs=. -o locales/messages.pot`
+2. `pybabel update -d locales -D messages -i locales/messages.pot`
+3. Open `locales/{language}/LC_MESSAGES/messages.po` and Translate msgs
+4. `pybabel compile -d locales -D messages`
+
+"""
+import asyncio
+from typing import Any
+
+from aiogram import Bot, Dispatcher, Router
+from aiogram import types
+from aiogram.filters.command import Command, CommandStart
+from aiogram.utils.i18n import gettext as _, I18n
+from aiogram.utils.i18n.middleware import I18nMiddleware, SimpleI18nMiddleware
+
+
+# class BotI18nMiddleware(I18nMiddleware):
+#     async def get_locale(self, event: types.Update | Any, data: dict[str, Any]) -> str:
+#         # here is your logic, ex. get language from redis DB.
+#         return 'en'
+
+
+bot = Bot(token="<Your token>")
+router = Router()
+dp = Dispatcher()
+# NOTE: basic middleware is provided. You can customize your middleware, ex. BotI18nMiddleware
+i18n_middleware = SimpleI18nMiddleware(
+    I18n(
+        path="locales",
+        default_locale="en",
+        domain="messages"
+    )
+)
+dp.update.outer_middleware(i18n_middleware)
+
+
+@router.message(CommandStart())
+async def start_handler(message: types.Message):
+    await message.answer(
+        _("Hello!. Write /language <new_lang>. Ex: /language ru")
+    )
+
+
+@router.message(Command("language"))
+async def change_language(message: types.Message):
+    """
+    This function dynamically changes language inside of handler
+    Handler input: /language <new_lang>. Ex: /language ru
+
+    Aiogram saves language context on start, so we should change language in runtime
+    """
+    new_lang = message.text.split(maxsplit=1)[1]
+    # change in runtime
+    with i18n_middleware.i18n.context(), i18n_middleware.i18n.use_locale(new_lang):
+        # all messages in this context will be translated to new_lang
+        await message.answer(_('Language was changed to {lang}').format(lang=new_lang))
+
+
+dp.include_router(router)
+
+
+async def main():
+    print("Bot started")
+    await dp.start_polling(bot)
+
+
+if __name__ == "__main__":
+    asyncio.run(main())