[lxgr]

> approximately 3 people set the browser language settings ever

But I'd guess most people select their preferred language when initially setting up their device, which usually informs their browser language, no?

> and nobody respects them

In my experience, many most multilingual sites do respect them! (This sometimes throws me off when the non-English version of a site is automatically/badly translated and I have to manually switch to English, but I can see how it makes sense for most users.)

[marginalia_nu]

To make matters worse, it's not uncommon for the language to be hard coded via the OEM version of the OS.

[lxgr]

This used to be true for Windows, but I don't think it is anymore. At least on the last version I used, I was able to change the UI language (but that was also marketed as an "Ultimate Edition perk" or something similar, so I'm not sure if OEM versions are still language-locked).

Where it probably gets tricky is for languages that operating systems are not commonly available in – users presumably have less of an incentive to set the correct locale if it does not make an immediate difference (assuming it is even offered in the setup dialog).