It was enjoyable that in Enterprise it took a while for the translator to start working, though I imagine it should've taken a lot longer than it did, at which point I'm giving them a bit of a pass for dramatic license. It would be hard for the computer to translate 30 seconds of speech of a completely unknown language into English, without any context whatsoever - they could say "why are your eyebrows so bushy?" or "hello, we're the Xalaxians." Maybe the aliens know Vulcan already or the UT sends them messages in one of a dozen languages they do know already? If there's interstellar commerce then it's likely aliens have come up with a common language for commerce, much like Latin, French, and English have served on Earth.