fix: negotiate Accept-Language with language-only subtag fallback (#1973)#1975
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) The Accept-Language locale selector matched header tokens by full identifier only, so a region-qualified top preference was dropped in favor of a lower-ranked exact match: a browser sending `ca-ES,es;q=0.9` was served Castilian instead of Catalan. Add a framework-owned `LocaleFromAcceptLanguage` selector (backed by a reusable `negotiate_accept_language` helper) that resolves each preference by full tag first, then by its language-only subtag, so the highest-quality acceptable language wins. Wire it into the locale selector chain in place of starlette_babel's `LocaleFromHeader`, whose matching is the upstream root cause. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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Upstream root cause reported: alex-oleshkevich/starlette_babel#16. This PR fixes it framework-side regardless of the upstream timeline. |
davidpoblador
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🤖 I have created a release *beep* *boop* --- ## [10.22.4](v10.22.3...v10.22.4) (2026-06-02) ### Bug Fixes * fast-path worker-health to skip CLI bootstrap ([#1974](#1974)) ([#1977](#1977)) ([ee77f6c](ee77f6c)) * load ProjectConfiguration deploy-config from .env ([#1970](#1970)) ([#1971](#1971)) ([13b67a7](13b67a7)) * negotiate Accept-Language with language-only subtag fallback ([#1973](#1973)) ([#1975](#1975)) ([0738181](0738181)) ### Documentation Updates * warn that backgrounded SSE tabs drop events and document resync ([#1978](#1978)) ([6bb1a91](6bb1a91)) --- This PR was generated with [Release Please](https://github.com/googleapis/release-please). See [documentation](https://github.com/googleapis/release-please#release-please). --------- Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
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Summary
Fixes #1973. The Accept-Language locale selector matched each header token against the supported locales by full identifier only, so a region-qualified top preference was silently dropped in favor of a lower-ranked exact match. A Catalan browser sending
Accept-Language: ca-ES,es;q=0.9,en;q=0.8was served Castilian (es) instead of Catalan (ca), and a bareca-ESresolved to nothing.The root cause is upstream in
starlette_babel.LocaleFromHeader, which never falls back to the language-only subtag (ca_ES→ca) even though the rest of the library (LocaleMiddleware._find_variant,negotiate_locale) is built around exactly that fallback. We're already on the latest release (1.1.0), so this fixes it framework-side now; the upstream behaviour is being reported separately.Change
negotiate_accept_language(header, supported)invibetuner.i18n: a pure helper that walks the header's tags highest-to-lowest quality and returns the first that matches a supported locale by full tag, then by language-only subtag. The highest-quality acceptable language wins;q=0tags and the*wildcard are skipped.LocaleFromAcceptLanguage, the selector wrapper, and use it in_build_locale_selectorsin place ofLocaleFromHeader.llms.txt,llms-full.txt.Tests
New unit tests in
tests/unit/test_i18n.pycover the negotiation (region-qualified top preference beats lower-q exact, bare region fallback, unsupported-top-token defer, exact region preservation, language-only → first supported variant,q=0skip, wildcard, empty/no-match, case-insensitivity, malformedq) plus the selector wrapper.test_locale_selectors.pyupdated to mirror the new selector. Full unit suite: 960 passed.Closes #1973