Accept-Language - HTTP | MDN
The Accept-Language request HTTP header indicates the natural language and locale that the client prefers. The server uses content negotiation to select one of the proposals and informs the client of the choice with the Content-Language response header. Browsers set required values for this header according to their active user interface language. Users rarely change it, and such changes are not recommended because they may lead to fingerprinting.
https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Accept-Language
