Tkinter i18n (中文即 key)

A lightweight, gettext-free i18n scheme for Tkinter apps. Chinese strings are the
dictionary keys; an _EN table holds English; unknown keys fall back to the
Chinese source so the UI never shows blank/missing text.

When to use

• A user wants a Tkinter tool bilingual (中文 / English) or multi-language.
• Need auto-detect of system language + a manual dropdown + "remember my choice".
• Avoid gettext (it does not survive PyInstaller --onefile freezing cleanly).

Pattern

1. Define t(key, *args) — returns _EN.get(key, key), then str % args if
   args present. Never raises on missing keys.
2. Keep one _EN = {...} table. Add an entry for every user-visible string.
3. _detect_lang() — Windows: ctypes.windll.kernel32.GetUserDefaultUILanguage()
& 0xFF == 0x04 → Chinese, else English. Fallback to locale on non-Windows.
4. Persist choice to ~/.workbuddy/APP.lang (zh/en); load at startup.
5. Manual switch: write the file, then restart the process
   (os.execv(sys.executable, [sys.executable] + sys.argv)) so every widget
   rebuilds with the new language. Per-widget live redraw is fragile — restart
   is simpler and reliable.

See references/i18n_template.py for a complete, runnable minimal app.

Wiring checklist

• [ ] Import t at top; wrap every user-visible string (titles, buttons,
  labels, messageboxes, status text, model display names, dropdown labels).
• [ ] Add a language ttk.Combobox (top-right) bound to the switch handler.
• [ ] LANG_ORDER = ["zh", "en"], LANG_NAMES = {"zh": "中文", "en": "English"}.
• [ ] Restart-on-change writes config then os.execv.
• [ ] Adding a language later = add a branch in _detect_lang + a new translation
  table + extend LANG_ORDER/LANG_NAMES.

Notes

• Frozen (PyInstaller) safe: no external .mo files, no gettext runtime.
• The language config path should live under ~/.workbuddy/ so it is shared with
  the agent's config dir, or under the app's own dir — pick one and be consistent.