It requires the website to actually handle its languages based on the locale sent from your browser. So if a website doesn't care at all about which language you have selected as your "preferred one", then nothing will happen.

But this could have been handled way better if you had created an Issue on GitHub. This would have allowed real conversation and with the website URL, you tested with, I would have been able to tell you if this website actually is "multi language" and does any switching based on the language sent by your browser.