a guy in my class is from france, so hes fluent in french and english, we had a cover teacher for chemistry for like...a term and for the entirety of the term the guy would be doing all his work in french and only talking in french and it annoyed the teachers so much it was great
I've met a couple clients who pretend not to speak English in their day to day life (the reason I know they speak English at all is because they do so to conduct business with me). They've lived in the US for longer than I've been alive, but they choose not to speak English most of the time. I find it annoying. I get when people are visiting the US and don't know English very well, but I think if anyone chooses to move to another country, they should assimilate to the culture. If I moved to another country I would learn the language (and I would learn the basics before even going there) and speak it whenever possible in order to not be a burden on the natives.