Parse Accept-Language header in wp_load_translations_early

[swissspidy]

Parse Accept-Language header when loading translations early where the current locale can't be fetched from the database.

Trac ticket: https://core.trac.wordpress.org/ticket/30049

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stale

[Copilot]

Pull request overview

Adds early-l10n fallback behavior by parsing the browser’s Accept-Language header when WordPress can’t yet determine the locale from the database, so the maintenance screen (and other early output) can be localized sooner.

Changes:

• Add get_locales_from_accept_language_header() helper to derive candidate locales from Accept-Language.
• Use that helper in wp_load_translations_early() to expand the locale candidates list.
• Add PHPUnit coverage for parsing behavior and expand the maintenance-mode E2E spec to assert a localized variant.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 5 comments.

File	Description
src/wp-includes/load.php	Adds formatting helpers and merges locales derived from Accept-Language into early-translation locale candidates.
src/wp-includes/l10n.php	Introduces get_locales_from_accept_language_header() to parse/sort language tags and map them to WordPress locales.
tests/phpunit/tests/l10n.php	Adds data-driven tests for get_locales_from_accept_language_header().
tests/e2e/specs/maintenance-mode.test.js	Adds a localized maintenance-mode assertion using a German locale.

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