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An audit found the client already i18n-first: one hard-coded UI string (the battle-scene aria-label, now keyed) and en/ru already share an identical 692-key set. - Persist the locale: i18n.setLocale writes localStorage (galaxy-locale) and the store boots from stored > browser detection > default, so a language switch survives reloads. - tests/i18n-completeness.test.ts: en/ru key-set parity, non-empty values, and locale persistence. - Docs: ui/docs/i18n.md; mark F3 done in ui/PLAN-finalize.md. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>