This question already has an answer here:
In the 4th season's premiere, the Way of the Warrior, Gowron utters the Klingon phrase
"It's a good day to die"
which Benjamin Sisko had to ask Worf to be translated first - why didn't the Universal Translator do its work?
There's a very similar, more generic question, but to my understanding that one doesn't indicate whether it merely means appearances of foreign languages to the viewer or actual in-universe non-translations.