[Agent] i18n: fill missing translations in all locales (~44% coverage today) #656

Problem and evidence

The non-English locales cover about 44% of the UI. In web/public/locales/, en.json has 2,645 leaf keys, while es/de/fr/it/ja/ko/zh/ru/uk/tr/nl/pl/pt-PT/ar have about 1,158. fil, pt-BR and zh-TW also lag. Missing keys fall back to English (web/js/i18n.js), so whole features show in English in every other language.

Biggest gaps, measured on es.json:

Expected behavior and scope

• Add the missing keys to every locale listed in web/public/locales/manifest.json, translated from en.json.
• Keep {placeholder} interpolation tokens exactly as they are, and keep any HTML and keyboard shortcuts unchanged.
• Use consistent terminology within each locale. Reuse the wording the locale already uses for terms like "stream", "recording", "detection" and "retention" (check the existing keys first).
• Product and protocol names stay untranslated: LightNVR, go2rtc, ONVIF, RTSP, WebRTC, HLS, MSE, MQTT, S3, PTZ, TOTP.
• Add a script or Jest test (web/tests/locale-coverage.test.js or similar) that reports per-locale coverage and fails if any locale has a key en.json lacks (orphans), or if placeholder tokens don't match en. Missing keys should only warn, so new English strings don't block CI.
• If this issue is too big for one PR, split it by namespace group (for example settings+system, live+setupWizard, events+investigation+collections+fleet, access+tokens+audit). Each PR covers all locales for its namespaces.

Acceptance criteria

• Every locale reaches ≥ 98% of en.json keys, or 100% for the namespaces covered by a partial PR.
• The placeholder and orphan check passes for every locale.
• Every JSON file is valid and keeps the existing key order and nesting style. No unrelated reformatting churn.
• Spot-check: switching to de, ja and ar in the UI shows no English on the Settings, Event Routing and Investigation pages.

Validation

• cd web && npm test (including the new coverage test) and npx vite build.
• Ideally a native speaker reviews ja/zh/ar/ko afterwards. Note in the PR that the translations were machine-produced.

Constraints and rollback

• Only touch the locale JSON files, plus the new coverage test or script.
• Rollback: revert. English fallback keeps working.