Exolinguistics
I love Star Trek (esp. The Next Generation), but one of its shortcomings is its stance on alien languages. The Original Series and TNG tend to handwave the problem away completely by means of the universal translator. I’m currently working my way through Enterprise, which at least acknowledges the problem to a certain extent, insomuch as they have an exolinguist on board and the universal translator is sometimes faulty, but it’s still completely naïve, given that Hoshi can learn alien languages faster than anybody can learn a human language.
If we assume that aliens will speak languages (which is not certain – telepathy might be used on other planets), I see no reason to assume they will be pronounceable, or even parseable, by humans. Without even leaving Earth, imagine that the songs of whales were a real language of human complexity – who’d be able to pronounce that?
Furthermore, human languages seem to fall in a specific category of languages, very similar to context-free languages (but slightly more complex in some regards and not using all the features in other regards); who knows whether this would be true for aliens, too? If their language adhered to a regular grammar instead, I guess we’d have no problems learning their language, but they’d be unable to learn ours.
I’m not saying communication would be impossible, but I think it might take good exolinguists months if not years to get anywhere, and I think in most cases communication would be restricted to very simple ideas, and in most cases it would take place through a computer which would introduce a delay. But I guess this wouldn’t make for very good television.