You are trying to call an unbound function; zxLolBoT is a class, not an instance. As such, the self parameter is not being passed in for you, and the method only received 2 arguments instead of 3 (with self being that 3rd argument).
self is already that instance, access the method on that to get a bound version:
@zxlolbot.botcommand
def mesaj(self, sender, args):
kime = "[email protected]/xiff"
self.mesaj_gonder(kime, str(args[0]))
0
solved missing 1 required positional argument