All relationships hit communication barriers at some point, so relationships between people with different native languages are bound to have a lot of funny and confusing moments.
Even someone whose fluent in multiple languages is likely to get confused by some slang words, aphorisms, or even modes of body language, and if you live with someone it can be fascinating to navigate the spaces where you both don't know what the other person is talking about.
When I first met my now wife, she thought every baby animal should be prefixed with puppy, as in puppy dog.
So the were puppy cats, puppy birds, puppy sheep, puppy horses etc... It was gold. It was so funny that nobody told her it was wrong.
She got me back by teaching me how to say "I'm tired" as "I'm stupid" in her language. So when we moved to her country to live, revenge was had.
EDIT: by popular demand, my wife is German.