While this is mainly from a Star Trek perspective, it could apply to other universes in SF as well (and even to our reality, really).
In this question the focus is on ships from 150 years apart communicating. But one comment there raises a bigger question.
If two ships are approaching each other in space, and they have never contacted each other before and have no knowledge of each other, how would they communicate with each other? I know if they know some of the same other races, they might have common protocols, but if there was no prior contact at all and no connections at all, how would they communicate with each other?