We know that Hogwarts is in Britain, and all students speak English. Thus all the spell we have seen have English dialect. But what about the wizards of countries outside Britain?
Like when Hermione went to France and Ron went to Egypt. I am sure none of those wizards cast their spells in English... but somehow this thing was never discussed or mentioned?
Does this mean that every spell one cast in English has its counter spell in other languages? Each one of the spells in each one of the languages? Then what about the spells that one wizard invents himself and never discloses in public, like Sectumsempra (Invented by Snape and there could be tons of others from other wizards)?
Does this also mean that other wizards of other countries may have invented spells of their own, in their own language which somehow they have kept secret? There should be a check on things like this. Does the ministry keep track of such spells? If yes then how?
