You see, that's the thing. The Shivans' electronics are so much more efficient than ours, it seems they were able to target us right away, while it took us a while to get to be able to target them. They could have easily scanned our vessels for anything that looked like a data storage device and could have been able to retrieve the pattern on it (in whatever format that may be, magnetic, flash memory, holographic). Them with they're complex EM language, highly evolved minds, and supercomputers could probably decode it and translate it fairly quickly. Especially if they scanned what was connected to the data storage device. They scan the rest of the computers on the ship to see how they work with the dsd, they build their own module to connect to their own computers, they get strange text, it's only a matter of time before they find an alphabet chart and a dictionary somewhere within. And anyone can read a dictionary, even if they don't speak that language. They find that this means that, they look up that, and find it means something else, and so on. They probably have supercomputers to do it for them. Just like a universal translator from Star Trek, pick out patterns and find out what words are equal to what other words.