feat: add i18n support for backend API and Telegram bot (#797)

* feat: add i18n support for backend API and Telegram bot

- Add comprehensive i18n support for all backend API error messages (zh/en)
- Add /lang command for Telegram bot to set language preference
- Add bilingual command descriptions for Telegram bot
- Support per-user language preference stored in KV
- Global push uses DEFAULT_LANG, user push uses saved preference

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

* fix: improve Telegram bot language preference feature

- Add internationalized message for disabled language feature
- Fix hardcoded English message in /lang command
- Optimize getTgMessages calls (reduce from 3 to 1 call)
- Remove verbose comments for better code clarity
- Add TgLangFeatureDisabledMsg to i18n (zh/en)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

---------

Co-authored-by: Claude <noreply@anthropic.com>

worker/src/mails_api/auto_reply.ts

@@ -1,11 +1,13 @@
 import { Context } from "hono";
 import { getBooleanValue } from "../utils";
+import i18n from "../i18n";
 
 
 export default {
     getAutoReply: async (c: Context<HonoCustomType>) => {
+        const msgs = i18n.getMessagesbyContext(c);
         if (!getBooleanValue(c.env.ENABLE_AUTO_REPLY)) {
-            return c.text("Auto reply is disabled", 403)
+            return c.text(msgs.AutoReplyDisabledMsg, 403)
         }
         const { address } = c.get("jwtPayload")
         const results = await c.env.DB.prepare(
@@ -23,17 +25,18 @@ export default {
         })
     },
     saveAutoReply: async (c: Context<HonoCustomType>) => {
+        const msgs = i18n.getMessagesbyContext(c);
         if (!getBooleanValue(c.env.ENABLE_AUTO_REPLY)) {
-            return c.text("Auto reply is disabled", 403)
+            return c.text(msgs.AutoReplyDisabledMsg, 403)
         }
         const { address } = c.get("jwtPayload");
         const { auto_reply } = await c.req.json();
         const { name, subject, source_prefix, message, enabled } = auto_reply;
         if ((!subject || !message) && enabled) {
-            return c.text("Invalid subject or message", 400)
+            return c.text(msgs.InvalidAutoReplyMsg, 400)
         }
         else if (subject.length > 255 || message.length > 255) {
-            return c.text("Subject or message too long", 400)
+            return c.text(msgs.SubjectOrMessageTooLongMsg, 400)
         }
         const { success } = await c.env.DB.prepare(
             `INSERT OR REPLACE INTO auto_reply_mails`
@@ -44,7 +47,7 @@ export default {
             subject || '', message || '', enabled ? 1 : 0
         ).run();
         if (!success) {
-            return c.text("Failed to auto_reply settings", 500)
+            return c.text(msgs.OperationFailedMsg, 500)
         }
         return c.json({
             success: success