In DB it was just described as a language Harry didnt recognize. He was a Kemmler apprentice, but that doesnt mean he has to have european heritage, especially in his magic. He's described as having a Cultured accent, so paint him educated and he could reasonably have studied most any dead language, or even have bargained with something inhuman and learned magic in some non-human dialect, you know The Language of Blood (or somethign less cheezy
). Id decide what flavor you plan to run with, and give him some obscure dead language from that region. Maybe he has a lot of aztec blood magic in his repitior, so he uses the language of the court shamen or some such.
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