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/import_duty_schedule.py

@@ -7,6 +7,7 @@ from telegram import Update
 from telegram.ext import CommandHandler, ContextTypes, MessageHandler, filters
 
 from duty_teller.db.session import session_scope
+from duty_teller.i18n import get_lang, t
 from duty_teller.importers.duty_schedule import (
     DutyScheduleParseError,
     parse_duty_schedule,
@@ -20,14 +21,12 @@ async def import_duty_schedule_cmd(
 ) -> None:
     if not update.message or not update.effective_user:
         return
+    lang = get_lang(update.effective_user)
     if not config.is_admin(update.effective_user.username or ""):
-        await update.message.reply_text("Доступ только для администраторов.")
+        await update.message.reply_text(t(lang, "import.admin_only"))
         return
     context.user_data["awaiting_handover_time"] = True
-    await update.message.reply_text(
-        "Укажите время пересменки в формате ЧЧ:ММ и часовой пояс, "
-        "например 09:00 Europe/Moscow или 06:00 UTC."
-    )
+    await update.message.reply_text(t(lang, "import.handover_format"))
 
 
 async def handle_handover_time_text(
@@ -39,18 +38,17 @@ async def handle_handover_time_text(
         return
     if not config.is_admin(update.effective_user.username or ""):
         return
+    lang = get_lang(update.effective_user)
     text = update.message.text.strip()
     parsed = parse_handover_time(text)
     if parsed is None:
-        await update.message.reply_text(
-            "Не удалось разобрать время. Укажите, например: 09:00 Europe/Moscow"
-        )
+        await update.message.reply_text(t(lang, "import.parse_time_error"))
         return
     hour_utc, minute_utc = parsed
     context.user_data["handover_utc_time"] = (hour_utc, minute_utc)
     context.user_data["awaiting_handover_time"] = False
     context.user_data["awaiting_duty_schedule_file"] = True
-    await update.message.reply_text("Отправьте файл в формате duty-schedule (JSON).")
+    await update.message.reply_text(t(lang, "import.send_json"))
 
 
 async def handle_duty_schedule_document(
@@ -60,11 +58,12 @@ async def handle_duty_schedule_document(
         return
     if not context.user_data.get("awaiting_duty_schedule_file"):
         return
+    lang = get_lang(update.effective_user)
     handover = context.user_data.get("handover_utc_time")
     if not handover or not config.is_admin(update.effective_user.username or ""):
         return
     if not (update.message.document.file_name or "").lower().endswith(".json"):
-        await update.message.reply_text("Нужен файл с расширением .json")
+        await update.message.reply_text(t(lang, "import.need_json"))
         return
 
     hour_utc, minute_utc = handover
@@ -77,7 +76,7 @@ async def handle_duty_schedule_document(
     except DutyScheduleParseError as e:
         context.user_data.pop("awaiting_duty_schedule_file", None)
         context.user_data.pop("handover_utc_time", None)
-        await update.message.reply_text(f"Ошибка разбора файла: {e}")
+        await update.message.reply_text(t(lang, "import.parse_error", error=str(e)))
         return
 
     def run_import_with_scope():
@@ -90,16 +89,29 @@ async def handle_duty_schedule_document(
             None, run_import_with_scope
         )
     except Exception as e:
-        await update.message.reply_text(f"Ошибка импорта: {e}")
+        await update.message.reply_text(t(lang, "import.import_error", error=str(e)))
     else:
         total = num_duty + num_unavailable + num_vacation
-        parts = [f"{num_users} пользователей", f"{num_duty} дежурств"]
-        if num_unavailable:
-            parts.append(f"{num_unavailable} недоступностей")
-        if num_vacation:
-            parts.append(f"{num_vacation} отпусков")
+        unavailable_suffix = (
+            t(lang, "import.done_unavailable", count=str(num_unavailable))
+            if num_unavailable
+            else ""
+        )
+        vacation_suffix = (
+            t(lang, "import.done_vacation", count=str(num_vacation))
+            if num_vacation
+            else ""
+        )
         await update.message.reply_text(
-            "Импорт выполнен: " + ", ".join(parts) + f" (всего {total} событий)."
+            t(
+                lang,
+                "import.done",
+                users=str(num_users),
+                duties=str(num_duty),
+                unavailable=unavailable_suffix,
+                vacation=vacation_suffix,
+                total=str(total),
+            )
         )
     finally:
         context.user_data.pop("awaiting_duty_schedule_file", None)