An intersteller empire's signals intelligence service would have entire departments of very smart people devoted to understanding, replicating and ultimately being able to interact with the computer technologies of alien empires. Figuring out the basis of the alien's IT technology wouldn't be that hard, you just get hold of civilian examples and get your engineers to figure out how it works. Working out how their communications technologies work would be harder and breaking their cryptography would be extremely challenging. But you throw enough brains, money and computer processing power at it, you could at least have a crack at it.
this. in Halo both the UNSC and Covenant knowledge of each other came exclusively from intelligence and salvaging components. AIs would also help massively considering (once again from halo) they fly entire capital ships single-handedly while figuring out how an unfamiliar FTL drive works, building a plasma-shaping weapon system from scratch, fending off onboard enemies and an enemy AI all at the same time.
AIs are the underappreciated badasses of sci-fi.