No one knows how the international laws governing supercriminals work, not even Law and the Multiverse. but we know Poland is not held responsible for actions of Magneto, Germany isn't responsible for the Red Skull (anymore), the US for Ultron, China for the Mandarin etc.

So clearly there is some mechanism. Might be as simple as reporting them to Interpol. But the X-men themselves have been considered close to supervillains by governments, so it probably not a huge leap.

At some point they are going to have to tell the Avengers too.