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contentVercel

Detect Language, Not Location

MUST

MUST: Pick the UI language from `Accept-Language` / `navigator.languages`, never from IP geolocation (VPNs, travel, and multilingual countries break that assumption), and still expose an explicit language switcher as the override.

Choose the UI language from Accept-Language or navigator.languages, never from IP geolocation

Bad

Good

Why it matters

Where a request originates says nothing about what the reader can read: VPNs, travel, corporate proxies, and multilingual countries all break the IP-to-language assumption. Accept-Language and navigator.languages carry the preference the user actually configured, ordered by priority — read those, and still expose an explicit language switcher as the override.

References

Built by Gleb Stroganov, design engineer at Evil Martians.

The rules come from other people's skills and guidelines — Vercel, Rauno Freiberg, @Ibelick, impeccable, Emil Kowalski, Tailwind, RAMS — each one credited on the Sources page. The work here is extraction and wiring: every rule is pulled into one corpus, given a good and a bad example you can operate, a MUST/SHOULD/NEVER rule an agent can paste, and a link back to where it came from.