Implement i18n middleware and add example.

examples/i18n_example.py

@@ -0,0 +1,57 @@
+"""
+Internalize your bot
+
+Step 1: extract texts
+    # pybabel extract i18n_example.py -o locales/mybot.pot
+Step 2: create *.po files. For e.g. create en, ru, uk locales.
+    # echo {en,ru,uk} | xargs -n1 pybabel init -i locales/mybot.pot -d locales -D mybot -l
+Step 3: translate texts
+Step 4: compile translations
+    # pybabel compile -d locales -D mybot
+
+Step 5: When you change the code of your bot you need to update po & mo files.
+    Step 5.1: regenerate pot file:
+        command from step 1
+    Step 5.2: update po files
+        # pybabel update -d locales -D mybot -i locales/mybot.pot
+    Step 5.3: update your translations
+    Step 5.4: compile mo files
+        command from step 4
+"""
+
+from pathlib import Path
+
+from aiogram import Bot, Dispatcher, types
+from aiogram.contrib.middlewares.i18n import I18nMiddleware
+from aiogram.utils import executor
+
+TOKEN = 'BOT TOKEN HERE'
+I18N_DOMAIN = 'mybot'
+
+BASE_DIR = Path(__file__).parent
+LOCALES_DIR = BASE_DIR / 'locales'
+
+bot = Bot(TOKEN, parse_mode=types.ParseMode.HTML)
+dp = Dispatcher(bot)
+
+# Setup i18n middleware
+i18n = I18nMiddleware(I18N_DOMAIN, LOCALES_DIR)
+dp.middleware.setup(i18n)
+
+# Alias for gettext method
+_ = i18n.gettext
+
+
+@dp.message_handler(commands=['start'])
+async def cmd_start(message: types.Message):
+    # Simply use `_('message')` instead of `'message'` and never use f-strings for translatable texts.
+    await message.reply(_('Hello, <b>{user}</b>!').format(user=message.from_user.full_name))
+
+
+@dp.message_handler(commands=['lang'])
+async def cmd_lang(message: types.Message, locale):
+    await message.reply(_('Your current language: <i>{language}</i>').format(language=locale))
+
+
+if __name__ == '__main__':
+    executor.start_polling(dp, skip_updates=True)