The language has been created by David J. Peterson, writer and language creator, president of the Language Creation Society. He created, among others, the Dothraki and Valyrian languages for the Game of Thrones TV series.
Answering a question on Goodreads, Peterson says that:
Verbis Diabolo is different from anything I've ever done. First, it's a posteriori, which means that all the words and grammar come from other—in this case, real world—sources. Specifically, the sources were Arabic, Akkadian, Middle Egyptian, Attic Greek, Latin, Farsi and Turkish. Second, VD was not intended to be a language proper. I looked at the language as an art piece. VD is supposed to be a language twisted in form; wrenched from Earth's languages. Many words that meant something in a given language are taken and reversed phonetically to produce the equivalent VD word. Sometimes the reversal came with a reversal in meaning, as with justa, from Latin, which becomes atsüü, "vile". Also pieces of words from many different languages will often be combined to produce portmanteaux which may have nothing to do with the original meanings of any of the parts.
In addition, though there are patterns in the language, sometimes the patterns are broken for no reason. A word which has meant the same thing every time one has heard it will suddenly have a new meaning in a new sentence for no discernible reason. Words will change orders to subvert previously attested patterns; words will be pronounced differently for no reason at all; the auxiliary, one of the few bits of predictability in the language, will move or drop out entirely.
All of this combines to produce something that doesn't sound an awful lot like a language, and I think that's true. It defies attempts to learn it, meaning that the only way to actually speak it is to be touched by the devil. In effect, that was the point.
So, yes, it is based on real languages and includes real words, but the meaning is not always the original one.