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Instead of using navigator.language (which often returns a regionless tag like "en", defaulting to US formatting), fall back to Intl.DateTimeFormat().resolvedOptions().locale which returns a fully resolved locale from the system/OS regional settings. Adds DateFormatter.defaultLocale as a static override for testing and future per-user preference support. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
jasonvarga
changed the title
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
jasonvarga
changed the title
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What & Why
DateFormatterwas usingnavigator.languageas the default locale, which often returns a regionless tag likeen. When passed toIntl.DateTimeFormat, this resolves to US formatting (MM/DD/YYYY) — affecting users in the UK, Australia, Europe, etc. who have their browser set to English without a region.The fix uses
Intl.DateTimeFormat().resolvedOptions().localeas the fallback instead, which returns a fully resolved locale from the system/OS regional settings (e.g.en-GBrather thanen).A static
DateFormatter.defaultLocaleproperty is also introduced, which takes priority when set. This is used in tests to keep assertions deterministic without mockingnavigator.language, and could serve as a hook for overriding via a preference if necessary.Changes
#locale = navigator.languagefield initializerlocalegetter now returnsDateFormatter.defaultLocale ?? Intl.DateTimeFormat().resolvedOptions().localesetNavigatorLanguage()forDateFormatter.defaultLocaleinbeforeEachFixes #14074
This PR intentionally does not introduce a preference. I'd like to see if this resolves the issue before introducing another thing.