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When your browser’s time zone and language don’t match your exit

Without asking for any permission, a web page can read your system time zone and your browser’s language list with a few lines of JavaScript, and your browser announces your preferred languages on every request in the Accept-Language header. A proxy only changes your exit IP. The time zone and languages come from your operating system and browser settings, so they stay the same with the proxy on. An exit in the US next to a time zone of Asia/Shanghai is therefore an inconsistency anyone can see from outside. Whether ChatGPT, Claude or other platforms use it, and how, isn’t public; IP Judge treats it as a low-weight environment signal.

At a glance: a proxy moves your IP onlyPage requests go through the proxy, so sites see the proxy exit. The time zone and language come from the operating system and browser settings; page scripts read them directly and request headers carry them unchanged, so they still say China after the exit moves abroad. At a glance: a proxy moves your IP only Exit IP Proxy controls it Browser Proxy app US exit IP Sites see whichever exit the proxy uses Time zone, language Out of its reach OS settings Browser Web page timeZone: Asia/Shanghai Accept-Language: zh-CN,zh The exit moved to the US; these didn’t Apple devices set the zone by location, not by IP.
A proxy relays connections; it doesn’t touch the system time zone or the browser’s languages. An overseas exit next to a China time zone and Chinese language is easy for a page to spot.

What a page can read

  • Time zone name: calling resolvedOptions().timeZone on Intl.DateTimeFormat() returns an IANA name such as Asia/Shanghai. MDN says the default is the runtime’s default time zone. In ECMA-402, an unset time zone becomes SystemTimeZoneIdentifier(), which ECMA-262 defines as the host environment’s current time zone.
  • UTC offset: new Date().getTimezoneOffset() returns the difference in minutes between UTC and local time, negative when local time is ahead of UTC (MDN). UTC+8 gives -480; in places with daylight saving time the value changes with the date.
  • Language list: navigator.languages lists your preferred languages in order, and navigator.language is its first entry (MDN).
  • The Accept-Language header: defined in RFC 9110, section 12.5.4, it tells the site which languages you prefer, optionally weighted with q values. MDN notes that it generally lists the same locales as navigator.languages, and that Chrome and Safari add language-only fallbacks, so zh-CN is followed by zh.

To reduce fingerprinting, Safari (always) and Chrome’s incognito mode list only one language, per the same MDN page. Section 17.13 of RFC 9110 names Accept-Language among the headers usable for browser fingerprinting, and notes that a set of languages can reveal things a user may consider private.

Why a proxy can’t change them

  • They’re produced on your device. The time zone comes from the system — MDN’s getTimezoneOffset page says it is the time zone of the host system the browser runs on. Languages come from browser or system settings; RFC 9110 requires browsers to let users control their language preference.
  • A proxy just relays connections. For an HTTPS site, the browser first opens a tunnel with CONNECT, after which the proxy is limited to blind forwarding in both directions (RFC 9110, section 9.3.6). Request headers travel inside TLS, so the proxy can neither read nor rewrite them. That holds in both system-proxy and TUN mode.
  • Automatic time zones don’t use your IP. Apple’s Mac User Guide says “Set time zone automatically using your current location” needs Location Services, and the iPhone User Guide says the time zone is set automatically and only needs changing by hand if Location Services is off or you have no service. Switching exits won’t move it.

What the platforms say publicly

Anthropic, OpenAI and Google all say in their privacy policies that they collect this kind of data. None says how a time zone or language affects verification, restrictions or bans:

  • Anthropic’s privacy policy (effective September 10, 2026) lists time zone setting, IP address (including location derived from it) and browser information under device and connection information. The purpose “to prevent and investigate fraud, abuse, and violations of our Usage Policy” lists this technical information among the data used.
  • OpenAI’s privacy policy (the version for people outside the US and Europe, updated February 6, 2026) includes time zone, country and user agent in usage data, and browser type and settings in log data; its purposes include preventing fraud and misuse. OpenAI’s help article on suspicious activity alerts gives sign-ins from unexpected locations or devices, sudden spikes in activity or settings changes, and more concurrent sessions than usual as reasons — not time zone or language — and suggests turning off VPNs and proxies while troubleshooting.
  • Google’s privacy policy covers browser type and settings and device type and settings, used among other things to detect and prevent fraud, abuse and security risks.

So the one certain thing is that platforms receive these values. How much they weigh in any risk decision can’t be seen from outside, and this article doesn’t guess.

How IP Judge checks and scores them

Both checks run on the home page and on the Claude, ChatGPT and Muse pages, in the “Browser time zone” and “Browser language” rows of “Browser and connection checks”. They are compared with the country of the exit Claude sees, or the exit that opened the site if that can’t be read; see Which IP do ChatGPT and Claude actually see?

  • Time zone: IP Judge reads the Intl time zone name. A China time zone (Asia/Shanghai, Asia/Urumqi, Asia/Hong_Kong, Asia/Macau and their legacy aliases) with an exit outside mainland China, Hong Kong and Macau is flagged amber, “Differs from exit region”, and added to the issue list. A US exit with a zone starting America/ (or Pacific/Honolulu) shows green, “Matches exit”. Anything else shows “Compare yourself”: the site keeps no country-to-time-zone table and makes no call. Asia/Taipei and Asia/Singapore don’t count as China time zones.
  • Language: the row shows the first three entries of navigator.languages, the Intl locale and the Accept-Language header our server actually received, but only the first language is judged. If it is zh, zh-CN or starts with zh-Hans, and the exit is outside mainland China, Hong Kong, Macau, Taiwan and Singapore, the row gets a blue note, “Differs from exit”; otherwise it reads “No conflict”. Traditional Chinese tags such as zh-TW and zh-HK aren’t flagged.
How IP Judge rates these two signalsA China time zone with an overseas exit is flagged amber and costs 5 points in the Claude score; a US exit with an Americas time zone is green; any other combination shows “Compare yourself”. Simplified Chinese as the first language with an overseas exit gets a blue note and costs 2 points. The Muse sign-up score uses its own weights. How IP Judge rates these two signals Right: points off the Claude score China time zone, exit abroad −5 Amber: “Differs from exit region” US exit, America/… zone No penalty Green: “Matches exit” Any other time zone No penalty “Compare yourself”: no verdict Simplified Chinese first −2 Blue note, exits abroad only; zh-TW exempt Muse score: Americas time zone 10, English 6. IP Judge’s own weights, not platform rules.
A time zone mismatch costs more than a language one: the time zone only follows system settings, while plenty of people abroad simply use Chinese.

In the Claude score these sit in the 10-point Browser section: a China time zone with an overseas exit costs 5, Simplified Chinese as the first language costs 2, and a TLS fingerprint that doesn’t match the User-Agent costs 3. In the Muse sign-up score the Browser section is worth 20: 10 for a time zone in the Americas (0 for China, 5 otherwise) and 6 for English first (2 for Chinese, 4 otherwise). The time zone weighs more because it only follows system settings, while many people abroad simply use Chinese. These are IP Judge’s own weights, not published platform rules — see the Method page.

How to align them, and what it costs

Time zone: turn off automatic setting in the OS and pick your exit’s location.

  • macOS: System Settings → General → Date & Time, turn off “Set time zone automatically using your current location”, type a city in the text field and press Return (Apple).
  • Windows: Start → Settings → Time & language → Date & time, turn off “Set time zone automatically” and choose from the Time zone drop-down; with it off, turn on “Adjust for daylight saving time automatically” (Microsoft).
  • iPhone: Settings → General → Date & Time, turn off Set Time Zone Automatically, then tap Time Zone City and search (Apple).
  • Android: in the Clock app, tap More → Settings → Change date & time → Time zone, turn off automatic setting and pick a zone (Google). Menus vary by manufacturer.

The cost: your device clock switches to the exit’s local time, and calendars and reminders display in the new zone. In a country with several time zones, such as the US, pick the one for your exit’s city. If you hop between exits in different countries, the time zone will always be wrong for some of them; sticking to one region is simpler.

Language: put English first and keep Chinese further down.

  • Chrome: Settings → Languages → Preferred languages, then reorder (Chrome Help). The interface language is separate: on Windows you pick “Display Google Chrome in this language” next to a language, so the menus can stay in Chinese; on Mac and Linux Chrome follows the system language.
  • Edge: Settings and more → Settings → Languages; Edge defaults to the system language (Microsoft).
  • Firefox: the Languages part of Settings, under “Website language”, where you choose languages in order of preference (see Firefox’s interface strings).
  • Safari follows the system’s preferred languages. On a Mac, drag a language to the top in System Settings → General → Language & Region; Apple says the primary language is used in macOS, apps and websites (Apple). On iPhone it’s Settings → General → Language & Region (Apple).

The cost: sites that choose a language from Accept-Language will serve you English first. For Safari users the whole device switches to English; on a Mac you can instead set a language for a single app under Applications on the same page, then check whether the Browser language row changes. Language is worth only 2 points in the Claude score, so if you depend on a Chinese interface, keeping it is a reasonable trade.

After changing anything, reload the home page to re-test. Beyond time zone and language, a page may also see another region through WebRTC or DNS.

FAQ

Will a time zone mismatch get my account banned?

No platform has said so publicly. IP Judge treats it as a small deduction; region, exit type and leaks carry far more weight in the score.

My exit is in Japan. Why does the time zone row say “Compare yourself”?

IP Judge only checks time zone consistency for US exits and keeps no table for other countries. Check that the zone name belongs to your exit’s country yourself — for Japan that’s Asia/Tokyo.

Can I change the time zone in the browser only, without touching the system?

Per MDN and the ECMAScript spec, pages read the host system’s time zone, and browser language settings don’t affect it. This article only covers the system setting that vendors document; after changing it, check the Browser time zone row on the check page.

In a private window only one language shows up. Is that normal?

Yes. Per MDN, Chrome’s incognito mode and Safari list a single language to reduce fingerprinting.

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