[maxmad64bis]

⚠️ base-red inherited: #15306

Summary

Translating new interface keys sends one request per language today, so 66 languages mean at least 66 requests while the concurrency setting only overlaps work inside each language. The per-request grouping already covered keys, never languages. This change adds an opt-in grouping of languages: without the flag every request stays exactly as before, and with it one request carries several languages and each broken line fails only its own language.

Related Issues

• No linked issue — batching covers keys but not languages in sync-ui-keys

Validation

• Change type: i18n
• Focused tests and category gates from the golden path
• npm run lint
• Reconciled with the current active release base; focused checks rerun afterward
• Production-code changes include a new or updated automated test in this PR

Tests Added Or Updated

• tests/unit/i18n-translate-backend.test.ts — multi-language response parsing by language code, single-request batching, broken-line isolation, and quote restoration.
• tests/unit/i18n-sync-ui-keys-locales-per-request.test.ts — flag parsing and defaults, locale chunking, placeholder union with divergent-source guard, planned-group requests with per-language retry, dry-run silence, and identical repeat runs.

Coverage Notes

N/A — no touched directory from the template list.

Reviewer Notes

• Behavior: without the flag the requests stay one language each; with --locales-per-request=11 six requests cover 66 languages, with live timing still to be recorded on a backend run.
• Merge: either order with feat(i18n): forward the optional reasoning control in the translation backend #15462, after perf(i18n): read synced locale keys by direct lookup #15466.
• Follow-up: run the live 66-language timing and record it; open the backlog count review at opening; defer the rate-limit daughter card unless 429 figures are requested.