> Then, as an affect of the first point, users will specify their most practical language, not some actual preference.
Where does this assumption come from? Given the fact that many (most? almost all?) sites don't honor the Accept-Language header, I doubt that there's much game theory going on in users' head when deciding this configuration.
They're right. Try to find a Dutch IT person with a laptop not set to English. Only a small fraction will realise you can set more than one language and put Dutch as a second, even though many struggle beyond basic reading comprehension in English. They're not picking it because they're just as good, much less better, at English compared to Dutch
We definitely pick languages that work as opposed to languages that we speak. Setting it to Dutch is just worse: UX doesn't fit, english search results wouldn't show up (way fewer results/content/info), and translations often don't make sense (imagine a button called "you shut it" on a modal window, it's a literal translation of one interpretation of the string "close it" but you'll be confused as to what that button will do)
The language set defaults to the language set in the OS, which is usually the preferred language for most users.
You have people working in IT who set their language to English for easier troubleshooting (i.e. not needing to Google error codes), but they're a small minority.
Anyone handling more than one language daily will be doing an explicit choice, and I wouldn't say they're a minority.
If your native tongue is Spanish but you live in the US for instance, the "preferred" language in your browser has IMHO a higher chance of being English. Same if you live in India probably.
I'd assume most WordPress based sites handling multiple locales will switch based on the Accept-Language ? Same if they let a framework handle the switch instead of a home-baked solution.
Even for auto-translated content, I wouldn't be surprised if it was off-the-shelf plugins that handle the switch.
All in all, I think it takes more effort to ignore the Accept-Language header. That won't prevent sites from tweaking it or doing their own cooking, but it kinda requires intent.
Where does this assumption come from? Given the fact that many (most? almost all?) sites don't honor the Accept-Language header, I doubt that there's much game theory going on in users' head when deciding this configuration.