Being a huge nerd with too much time on his hands, I've own a few different books about the Klingon language. I don't actually speak Klingon, but I can translate reasonably complicated chunks of text into passable Klingon given some time and my copy of the Klingon Dictionary. So, one of the things I like to do in the Star Trek RPG campaign I run is to slip in Klingon dialogue when the PCs run into Klingons.
In countless episodes of TNG and DS9, Klingon seems to be the only language which is translated, at best, haphazardly by the universal translator. What I mean by this isn't that the UT can't translate Klingon, of course, but that the writers found it convenient to insert snippets of the Klingon language into the dialogue, despite the fact that every other alien language gets translated automatically for us without comment. :D So, when I insert snippets of Klingon into my RPG games, I figure I'm following a time-honoured Trek tradition.
No doubt as a result of my ability to roleplay a big stupid oaf to perfection, my players have enjoyed their interactions with Klingon characters in my campaign quite a bit. As a result, some of them have decided that they'd like their characters to pick up ranks in the Klingon language. Fearing that I would be deprived of my ability to have NPCs slip into Klingon without offering a translation to my hapless players, I replied that they were welcome to take ranks in Language Klingon... so long as they went out and learnt Klingon, because any conversations which were going to take place in Klingon in my campaign would damn well be roleplayed in Klingon! ;)
I was wondering if anybody had any interesting language stories from their own Star Trek campaigns, whether it be actually talking at the gaming table in Klingon, Vulcan or some other equally tragic language, or whether it be an amusing story about the PC's UTs breaking down, I'd like to hear it.