Hypothesis: original (probably Latin) incantations were aliased to "Wingardium Leviosa" and similar because it was easier for Hogwarts students to learn.
Evidence:
Powerful wizards still use some Latin spells. Perhaps only up to 7h year magic was aliased?
We did not see any non-English wizards cast spells yet. It's likely (and fits into the setting) there are other syntaxes.
Due to the Interdict of Merlin, it's possible the Latin alternatives are lost.
The aliasing could be common knowledge among wizards, but not muggleborns. That could explain ... (read more)
One 10,000 year old human might be able to do it, though.