One thing that I think always confuses me about any science fiction work that deals with Humans meeting Aliens for the first time is that it seems to assume it's all on us to figure out a common language. I have to admit, my assumption if that if some species is sufficiently advanced to figure out interstellar travel they'd likely be able to decypher our language and find a way for us to communicate.
The story sorts this out. Absent an interpreter, you necessarily need to be able to talk to someone who knows the other language so that you can query them, etc. Realistically, there's no way to intercept or interpret communications as the protocols are almost impossible to figure out (that is another layer of 'language'). Let say an alien intercepts a TV signal, can they convert it back to video? It is almost imposs…
Messages don't exist by themselves, but are layered. Eg. To understand that a radio signal is a video I need to also understand video protocols, RF communication, etc.