The official English versions of Negima have never been especially consistent, but this omnibus is the worst offender by far. The dialogue is fine, but the translators screwed up the magic pretty badly.
Various spells have been renamed for no reason whatsoever. The way the Greek spells were written changed between two chapters that were in the same volume, never mind the same omnibus, and neither of those two translations were done in the same way as in previous omnibi (with one exception, they were always written with Greek lettering).
This is supposed to be the final version of Negima, so is it too much to ask that they pick a style and stick to it?
Then there is the mangled Latin. Not only did they mess up spells, but they messed up ones that they had never had trouble with in the past.
*Hint regarding Setsuna's artifact* the first word is Latin, and is spelled "Sica."
*Hint regarding Sagitta Magica* there is no letter K in Latin. "Sagita Magika Sirius Rukis" (all four words misspelled) is poorly translated Japanese. "Sagitta Magica Series Lucis" is proper Latin. There's just no excuse for this one.
Perhaps I'm nitpicking, but they CAN and HAVE translated these correctly. There is no reason other than pure laziness for work this shoddy and inconsistent.