Why wouldn't people have their language set correctly? Usually your browser language defaults to your system language, and presumably when you bought your computer, you selected your preferred language during the initial setup. If you had your browser set incorrectly, you would probably have dealt with that problem immediately when you saw all the menus and such in an unfamiliar language.

Perhaps some multilingual users might have one of their secondary language(s) set instead of their primary/preferred one, but at least it'll be a language they speak.

More importantly, even if the user has their browser screwed up, it's something that can be easily fixed on their end. But on sites that set language based on location, there isn't such an easy fix available; short of relocating or using a VPN, people in OP's situation are kinda screwed.