I get strange languages sprinkled through my Gemini responses, including some very obscure ones. It just randomly changes language for one or two words.

Is it possible the "vector" is more accurate in another language? Like espirit d'esclair or schadenfreude, or any number of other things that are a single word in a language but paragraphs or more in others?

Possibly. I have seen Claude switching to Russian for a word or two when it is about revolution!