Intl's default locale is a UI locale desktop Chrome ships
Under the Google Chrome brand on desktop, the Intl default locale is one of the UI locales Chrome ships ('en-US', 'en-GB', 'es-419', 'tr', 'de' and so on). N/A for other brands, other engines and mobile (severity: warn).
What a detector infers
Chrome's Intl default locale — what new Intl.DateTimeFormat().resolvedOptions().locale returns — is not the operating system's region. The browser resolves the system language against the UI locales it ships (55 on desktop), passes the result to every renderer, and ICU's default is set from it. So a Turkish system gives 'tr', Mexican Spanish 'es-419' and Canadian English 'en-GB': always a member of that list.
Measured on genuine Chrome with six Linux system locales and five Windows --lang values, every result was a shipped UI locale. The DevTools protocol's locale override, which is what Playwright's locale option uses, sets ICU's default to the raw tag instead: locale 'de-DE' produces 'de-DE', a regional tag desktop Chrome never resolves to.
In the audit's corpus, at least 18 Chrome captures carry such tags — tr-TR six times, et-EE three times, and es-MX, fr-FR, pl-PL, ko-KR, uk-UA and vi-VN. The row is limited to the Google Chrome brand, because Edge resolves to its own regional locales (measured: 'en-NL'). It differs from intl-locale-coherence, which checks that the Intl constructors agree with one another: they can all agree and still name a locale Chrome does not ship.
How to resolve it
Do not set the language with Playwright's locale option or Emulation.setLocaleOverride. Launch Chrome in that language instead — with --lang on Windows, or with the LANGUAGE or LANG environment variable on Linux, where --lang is ignored — and the browser resolves it to a UI locale exactly as it does for a person.
Nearby checks in Environment & locale
- Exactly one voice is the default, and it is the first
voice-default-is-firstChromium assembles one voice list — the operating system's voices first, then extension voices such as Google's network voices — and marks… - Google's network voices arrive as Google's exact set
google-voices-exact-setBranded Google Chrome on Windows, macOS and Linux adds a set of network voices from a component extension whose manifest lists exactly 19 of… - The local voices come from the claimed OS's speech engine
local-voice-vendor-vs-osVoices marked localService are the host's own speech engine, enumerated by the browser from the operating system, and their names say where… - The browser's own UI strings are in the language Intl resolves
validation-message-vs-intlThe messages a browser writes itself — 'Please fill in this field.' under an empty required input — come from the renderer's resource… - MediaCapabilities powerEfficient agrees with WebCodecs prefer-hardware
power-efficient-vs-webcodecsMediaCapabilities.decodingInfo() reports whether decoding a format would be power-efficient, and WebCodecs' VideoDecoder.isConfigSupported()… - A playback AudioContext buffers more than an interactive one
playback-hint-buffers-moreAn AudioContext created with latencyHint 'playback' asks for a larger buffer than one created with 'interactive', and Chrome honours the… - AudioContext latencies are values Chrome's audio stack can produce
audio-latency-render-stateTwo AudioContext latencies are produced by the audio stack at particular moments, and their values are constrained in ways a constant is… - A granted geolocation fix carries a real accuracy
geolocation-has-accuracyEvery position a real location provider returns comes with an accuracy: the radius, in metres, within which the true position probably lies.
Clearcote is a browser built for fingerprint coherence
It is a Chromium fork, maintained by the same people who wrote this reference. It ships as a compiled browser rather than as a stealth script injected into someone else's — which is a description of how it is built, and is not an argument about how it behaves on this check.
This audit takes no position on how Clearcote scores on Environment & locale checks, on this one, or anywhere else. It has no baseline corpus of other people's fingerprints to rank you against and no vendor scoreboard — nearly every check is self-referential, asking one browser the same question through two independent APIs and reporting whether both answers can be true at once. It runs identically on any browser, including ours. Run it on yours and read the result yourself.
See the other checks in Environment & locale — the family intl-is-a-chrome-ui-locale belongs to.