There is a great deal of "overlap" when it comes to knowledge. Where do you draw the line between magic and science? To the thoroughly uneducated, there *is* no difference. Thus, in Europe, the idea grew pervasive that magic, hidden knowledge, was (like *all* other hidden knowledge) to be found in Latin texts. Additionally, Latin was the language of The Church, and what is more magical than the miracles of Christianity (to a Christian, anyway)? Thus, magic and Latin were inseparable in the minds of Western Europeans for lots and lots of centuries.
Nearly *all* of the really famous magicians in Europe up until the modern age used Latin for their spells (there are a few Scandinavian and Welsh exceptions). This became so thoroughly ingrained in our Western culture that you can hardly find a TV show or movie - at all - that does not use Latin for the casting of spells.
So, JKR was just following the *very* well-established and common tradition. I would have been far more impressed if she, like the Scandinavians and Welsh, made music the language of magic....
Jim
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