If they have a universal translator, like they do in Star Trek, it would be a good assumption that the data would be on their main frame. The problem is they'll have no one to talk to, or very few, as both the legal and religious professions have largely given up the language. I don't think you'll get away with using Latin as an alien language as, in spite of what I've written before, they'll be quite a few people who will recognize it. However, if you can plant the idea that the aliens visited Earth back in Roman times you may get away with it as that was then the lingua franca. Sorry I can't be of any more help.