In my experience these are often configured wrong, because browsers are guessing settings based on the locales used by the operating system, and because users d

In my experience these are often configured wrong, because browsers are guessing settings based on the locales used by the operating system, and because users don't know how to configure it because it is really hidden away. For the cases I see it is technical minded people that speak another language than Danish, that buy (or inherit) a laptop with Windows on Danish, so the browser infers its settings from the operating system, and now you can no longer trust this header. But it might be just as wrong as guessing language based on IP-location, so there are not really a good out-of-the-box solution, so every website will have to build their own selector maybe with input both from the browser headers and from the IP-geolocation.