They have extradition agreements in Kazakhstan, and I think the same is true in some countries in the Middle East, such as Saudi Arabia and Egypt. They rounded up Uighurs and sent them back. I don't know the inner workings of how that has gone on, especially in the Middle Eastern countries. I know that in Kazakhstan and other central Asian republics, there are formal agreements that are part of the Shanghai Cooperation Organization that people signed onto in the early 2000s.
That's how it works there. In western countries, I don't know.