Do you think mutants only exisit in America? is it possible for China or the U.K. to have any types of mutations?

They probably would only have Ghouls.

Yeah, there's probably only ghouls and other irradiated creatures in the rest of the world. FEV was only in the US, so no Super Mutants anywhere else.
I'm not sure if the Army deployed Deathclaws before the bombs. That's what Deathclaws were intended for, but there might not have been time. If Deathclaws were deployed in China, they might have spread to the rest of Asia, and possibly Europe.