feat(i18n): add English support for host-side chat messages

Wrap all user-facing chat text in src/channels with a host-side t()
translator (Chinese is the identity default, so untranslated text is
always sent verbatim in Chinese). English is selected via the host
plugin config `language: en` or the DSH_IM_LANGUAGE environment
variable, and the settings UI keeps following the DSH web locale.

- add src/channels/shared/i18n.mjs with setImHostLanguage/t() and a
  Chinese-key -> English dictionary split by area (shared + channels)
- complete the English dictionary for every t() key in src/channels,
  including the feishu channel (welcome/help, repair flow, interactive
  cards, watch flow) and the shared command/approval/stream text
- wrap previously untranslated chat-facing strings in feishu bridge,
  feishu runtime, editable-message-stream, harness-client,
  connection-test and image-prompt
- dedupe dictionary entries that existed in multiple channel files and
  canonicalize conflicting translations into the shared dictionaries
- extend the i18n unit test to decode string-literal escapes so keys
  containing \n are checked correctly
- document the language switch in README.md, README.en.md and
  CHANGELOG.md, and rebuild lib/index.js

Added English support for bot chat messages across all nine IM
channels and AI Office without changing any Chinese output.

README.en.md

@@ -190,7 +190,7 @@ If the Slack desktop app has no native Slash Command registered with the same na
 
 - Registers one **IM Bot** settings page containing nine IM channels and one AI Office Connector.
 - Maintains the Host, client, and runtime sources for all nine channels and the Office Connector in this repository without external standalone plugins.
-- Follows the DeepSeek Harness language preference and switches the settings UI live between Chinese and English.
+- Follows the DeepSeek Harness language preference and switches the settings UI live between Chinese and English. Bot chat messages follow the Host's `language` config (Chinese by default; `en` switches them to English), with Chinese always as the fallback so untranslated text is sent verbatim.
 - Uses logos for WeChat, Feishu, DingTalk, WeCom, QQ, Slack, Telegram, Discord, WhatsApp, and AI Office navigation without enable/disable switches.
 - Keeps RPC endpoints, credentials, connection supervision, and session mappings isolated by IM channel; the Office Connector separately owns Device credentials, Job leases, approval waits, and concurrency limits.
 - Returns only QR codes, the public Slack Manifest, redacted status data, and access modes or allowlist identifiers explicitly saved for the current Telegram or WhatsApp bot. Manually entered secrets and Tokens travel one way to the local Host; no RPC response returns App Secrets, `bot_token`, DingTalk `client_secret`, WeCom Secrets, QQ `app_secret`, Slack Bot/App Tokens, Telegram/Discord Bot Tokens, WhatsApp linked-device keys, AI Office Device Tokens, or other raw user identifiers observed from platform messages.
@@ -215,6 +215,18 @@ IM management RPCs accept loopback browsers by default. When a Web profile is de
 
 `trusted-host` reuses Harness's Host/Origin fence; it is not user authentication. Anyone who can reach that LAN authority can inspect bot status, scan or submit application credentials, reconnect bots, and remove bots. Enable it only on a trusted network.
 
+### Bot chat message language
+
+Bot chat messages are in Chinese by default. To switch them to English, set `language: en` in the plugin config (also accepts `en-US` or `english`), or set the `DSH_IM_LANGUAGE=en` environment variable:
+
+```yaml
+- id: xmanrui-dsh-im
+  config:
+    language: en
+```
+
+Without a setting, Chinese is used. Chinese is always the fallback language — any text missing from the English dictionary is sent verbatim in Chinese, so this feature never changes the behavior of existing Chinese users.
+
 ---
 
 ## Contact