Bucky knowing at least 31 languages according to CACW, super serum brain enhancements and the fact he learned Xhosa in Wakanda, leads me to believe he must have the fucking gnarliest of language blurring. You know when you can't seem to figure out how to word something in one language so you skip over to a different one but wait no one knows that...
I also don't think English would be Bucky's default language anymore. It's his birth language, sure, but Russian is probably the language he defaults to now after 80 years right?
So if Bucky's ever delirious for whatever reason, extreme tiredness, magic, super drugs or whatever who knows, do we think he talks in the most insane blend of languages, does he say a sentence in Japanese then switch to Korean and then to Polish, do we think he'd point blank say "I'm sorry I don't speak English" in English to his English speaking friends or teammates because he thinks in Russian and about fifteen other languages before he gets to English, and then goes "oh wait I do" or...?