User Language

User language is the preferred language set in a user's browser or device, sent with each request as a hint of the language the user expects.

User language serves localization decisions: if a large share of the audience has a browser language other than the site's primary one, a multilingual version may be needed. But this signal has two weaknesses that must be seen honestly. First, the browser language is not necessarily the user's real preferred language; many keep their device on English while reading Persian, so the data under- or over-states the preference. Second, user language is not the same as geolocation and should not be conflated; a user in Iran can have an English browser and vice versa. So user language is a supplementary hint alongside geography and behavior, not a definitive basis for a localization decision; the best confirmation is always real behavior, such as which language version of a page users actually choose and follow.