Complete and maintain frontend i18n translations for this project. Covers finding missing translation keys, detecting untranslated entries, and adding translations for all supported locales (en, zh, zh-TW, fr, ja, ru, vi). Use for any task involving frontend locale files, missing translation keys, untranslated UI text, `t(...)` keys, `useTranslation()`, static i18n keys, button/label/ toast/dialog/placeholder/validation copy, or adding/fixing even a single i18n key. Use when review findings mention missing i18n, when new UI text needs translation, or when the user asks to add translations, fix i18n, or complete missing translations. Always load and follow this skill before translating, adding locale keys, or editing frontend i18n files.