And what could the dragon language be? We know it's probably used by thu'um users, but which type of dragons would use it?
My guess is it's whichever type of dragon we're fighting now, since as I understand it, Dovahkiin is a word in said language and it's what they use to call "The only one they fear", which seems likely, given what we know so far, to be the player character.
Although we don't know what type of dragon we're dealing with in Skyrim, yet, all we know is that there will be dragons. Maybe they'll be red, maybe they'll be black, or maybe there'll be more than one type, only time will tell.