No I think that would BE the point? You haven't translated their language, so you cannot use metagaming knowledge to deduce what the threat level is.
I don't think it would actually give you the gibberish message, though. I think the system would just tell you that you have received an unintelligable communication from somewhere.
My question is, are there other potential unintelligable messages you can receive such as "Hello! How are you? Welcome, friend!" so that the fact you receive such a message does not immediately make you realize that you are in another race's claimed space? Perhaps all "first contact" messages should look the same, so you can't tell the difference between a friendly greeting and a trespass warning.