Add a new UI language/locale to the claude-code-gui webview i18n system, or extend/verify an existing one. Walks a contributor (or agent) through creating the per-namespace translation JSON files, registering the locale, and verifying parity — consistently with how the shipped locales are structured. Use when someone wants to translate the UI into a new language, add a locale, or contribute translations. Trigger on: 언어 추가, 로케일 추가, 새 언어, 번역 추가, 번역 기여, add language, add locale, new language, translate the UI, contribute a translation, i18n locale.