On the topic of languages, I feel a bit differently than most of you, I feel that instead of there being different languages between Rhakhaan, Xa-ar, Wulris, & Tanara, there would be just local accents of a base language. Meaning, it would be more like English, as spoken by Americans, Irish, Scottish, and the English.
My reasoning for this is that these are very obviously highly conservative cultures; think about it: they have been largely static in technological and population growth for around 6,000 years. And, they started out with a higher tech-base than we here on Earth had 6,000 years ago - at lest, most of them did. So, why are they not in rocket-ships going to other planets? Why are they still mostly in the middle-ages, with only a few instances of renaissance era technology?
Language changes when it needs to; when new concepts and ideas are introduced. In such static cultures the language would not change so much, I don't think. So, while there should be different languages across Kulthea, these would mostly be tied to different races and ethnic groups, but not necessarily due to distance and time. Not that there wouldn't be some difference between the languages used by a race/ethnic group that lives in different areas on the planet, but that maybe, just maybe, these differences aren't enough to call them different languages altogether.
Just a though.
Plus: It sucks when the PCs can't speak with the locals (trust me, I am dealing with that now), it makes it really hard - which is why all the alien humans on Stargate spoke English, even though that language hadn't been created when they got separated from Earth.