[Feature Request] Add i18n / locale support for UI strings (Korean and other languages)

Claude Code currently hardcodes all UI strings in English — spinner verbs
(Thinking, Pondering, Pontificating, …), status messages, system prompts,
and notifications. There is no locale setting, no CLAUDE_LOCALE env var,
and no settings.json field for language.

Request: official i18n support so non-English users can localize the UI.

Suggestions:

1. Add a locale field in settings.json (e.g. "locale": "ko") that switches

built-in UI strings to a translated set.

1. Ship community-translatable resource files (JSON/po) for spinner verbs,

status messages, and notifications.

1. Honor standard env vars like LANG / LC_ALL as fallback.
2. Allow per-string override via settings.json — the existing spinnerVerbs

field is a great precedent; extend the same pattern to other UI strings.

Thanks!