I always put that down to each show being only an hour long; they had to skip all that stuff but the assumption was it still happened, as even with a universal translator there's going to be misunderstandings before communication becomes smooth
Actually the UT is depicted as being capable of directly translating most languages perfectly, even if they haven't been encountered before.
Species like Darmoks are said, or at least implied, to be rare in the galaxy, where translating their language (which the UT still does) doesn't result in clear communication.
Cultural differences still matter and are shown to be big-time issues across the galaxy, but it almost never has to do with the languages they speak.