Add internationalization support and enhance language handling

- Introduced a new i18n module for managing translations and language normalization, supporting both Russian and English.
- Updated various handlers and services to utilize the new translation functions for user-facing messages, improving user experience based on language preferences.
- Enhanced error handling and response messages to be language-aware, ensuring appropriate feedback is provided to users in their preferred language.
- Added tests for the i18n module to validate language detection and translation functionality.
- Updated the example environment file to include a default language configuration.

duty_teller/handlers/commands.py

@@ -8,6 +8,7 @@ from telegram.ext import CommandHandler, ContextTypes
 
 from duty_teller.db.session import session_scope
 from duty_teller.db.repository import get_or_create_user, set_user_phone
+from duty_teller.i18n import get_lang, t
 from duty_teller.utils.user import build_full_name
 
 
@@ -36,21 +37,23 @@ async def start(update: Update, context: ContextTypes.DEFAULT_TYPE) -> None:
 
     await asyncio.get_running_loop().run_in_executor(None, do_get_or_create)
 
-    text = "Привет! Я бот календаря дежурств. Используй /help для списка команд."
+    lang = get_lang(user)
+    text = t(lang, "start.greeting")
     await update.message.reply_text(text)
 
 
 async def set_phone(update: Update, context: ContextTypes.DEFAULT_TYPE) -> None:
     if not update.message or not update.effective_user:
         return
+    lang = get_lang(update.effective_user)
     if update.effective_chat and update.effective_chat.type != "private":
-        await update.message.reply_text("Команда /set_phone доступна только в личке.")
+        await update.message.reply_text(t(lang, "set_phone.private_only"))
         return
     args = context.args or []
     phone = " ".join(args).strip() if args else None
     telegram_user_id = update.effective_user.id
 
-    def do_set_phone() -> str:
+    def do_set_phone() -> str | None:
         with session_scope(config.DATABASE_URL) as session:
             full_name = build_full_name(
                 update.effective_user.first_name, update.effective_user.last_name
@@ -65,27 +68,33 @@ async def set_phone(update: Update, context: ContextTypes.DEFAULT_TYPE) -> None:
             )
             user = set_user_phone(session, telegram_user_id, phone or None)
             if user is None:
-                return "Ошибка сохранения."
+                return "error"
             if phone:
-                return f"Телефон сохранён: {phone}"
-            return "Телефон очищен."
+                return "saved"
+            return "cleared"
 
     result = await asyncio.get_running_loop().run_in_executor(None, do_set_phone)
-    await update.message.reply_text(result)
+    if result == "error":
+        await update.message.reply_text(t(lang, "set_phone.error"))
+    elif result == "saved":
+        await update.message.reply_text(t(lang, "set_phone.saved", phone=phone or ""))
+    else:
+        await update.message.reply_text(t(lang, "set_phone.cleared"))
 
 
 async def help_cmd(update: Update, context: ContextTypes.DEFAULT_TYPE) -> None:
     if not update.message or not update.effective_user:
         return
+    lang = get_lang(update.effective_user)
     lines = [
-        "Доступные команды:",
-        "/start — Начать",
-        "/help — Показать эту справку",
-        "/set_phone — Указать или очистить телефон для отображения в дежурстве",
-        "/pin_duty — В группе: закрепить сообщение о дежурстве (нужны права админа у бота)",
+        t(lang, "help.title"),
+        t(lang, "help.start"),
+        t(lang, "help.help"),
+        t(lang, "help.set_phone"),
+        t(lang, "help.pin_duty"),
     ]
     if config.is_admin(update.effective_user.username or ""):
-        lines.append("/import_duty_schedule — Импорт расписания дежурств (JSON)")
+        lines.append(t(lang, "help.import_schedule"))
     await update.message.reply_text("\n".join(lines))