I have the same problem with Spanish. I took a few years of it in high school, and don’t really speak it at all anymore. But, when speaking Japanese if my brain can’t find the Japanese word I’m looking for before it can find the Spanish word, out comes the Spanish word.
“El Bano wa doko desu ka?”
I’ve heard from a few people the third language is the worst. Once you get used to juggling, that sort of mixup almost never happens, and it’s all downhill for picking up new languages.