While annoying, I don't even care about websites setting the wrong language as default. What I absolutely HATE, though, is websites and apps that FORCE you to view them in a certain language, based on either location or on OS locale.
Google Maps is the worst. I live in Israel, so I obviously want to see street names in Hebrew. My Android device locale is set to English (Because that's the way I prefer, and I also rather not see everything flipped because of the RTL nature of Hebrew). This FORCES me to view street names in English, and there simply NO WAY around it other than changing the device language. It has been this way for years, and it's painful. Why not just let us modify the language on per-app basis?