[quote=@A Heretic]
I mean, Walden isn't practicing demonic magic, it's just black magic and necromancy. So sure you might get whiffs black magic if he performs it near the group but if he's trying to hide he'll definitely not do it while in the company of a GMO demon and a purifier. The dead language is as old as writing, the book showed up after the first written language. I can't go too much into detail Nariata knows the full details as GM I felt it would interfere the least with him to share, plus he asked. 
[/quote]

It's not as though demonic and black magic are completely unrelated, at their core they're both basically the art of manipulating the powers of the underworld. Demonic is simply naturally occurring while necromantic has to be essentially converted from standard magicks.

Does this language appear anywhere else other than the book?