One more time:
nowhere in TOS is it
ever established that Uhura is some sort of brilliant "language expert." She's an expert on communications technology and very skilled at her job, but point to the episode where she's previously shown to be fluent in Klingon or any other alien language. The popular notion that she's a super-linguist comes from fanon
, not the actual shows or movies. It's a fan theory at best. (At least until the reboot.)
Yes, one can certainly make a case for why it would behoove a Starfleet communications officier to be a trained linguist as well, but the fact remains ST VI was hardly in error for not being consistent with something that had never actually been established onscreen in the first place!
And, yes, I love
The Undiscovered Country. It's my third-favorite Trek movie, after Khan and the whales. (I guess I really like Nicholas Meyer's take on Trek.)