[@Lord Orgasmo]
I would suppose its based on the lineage and caste. Lessers having a simple understanding like animalistic grunts and verbal mannerisms while greaters could have anything from a specific language, a shapeless language that can only be spoken with a forked or [u]>[/u]two tongues, or even telepathy.

I'm not a gm, but everything I've said about demons and such so far is just my barest understanding of para-dimensional zoology.
Until I'm corrected by a gm, I'll just be a self-righteous jerk as assume I'm right.
>_>

Sorry in advance.
My CS was accepted, so at the very least, there is a link between Latin and demonic script. In some way, there might [i]technically[/i] be a language for demons. Though humanity has separate languages, so who could possibly tell what dialects and branching languages demons have.