If I may share some random thoughts...
I really hope they don't carry on from Reach in having the Covenant speak native tongues. The point of having the Covenant speak their respsective languages in Reach was clear; they were meant to be portrayed as alien invaders more than they were in any other Halo game, giving them a darker and more threatening tone. It worked by successfully turning the mind back to when you couldn't undertstand what they were saying (the Elites, at least) in the first Halo.
But I want the familiarity back again; when I first played Halo 2 and I heard the Elites speaking in understandable words, being called "Demon", there was this awesome feeling of having infamy among the Covenant, giving them relatable qualities. Hopefully that's what they're still interested in for Halo 4, instead of the blank slate alien menace.