Wat Would happen if an country government used nuclear weapons against its own citizens to end country wide riots against current government?

I don’t see something like that happening, it seems very unrealistic. If anyone were stupid enough to do that, they’d probably not only kill the people in the direct vicinity of the weapon, but would also kill millions of others outside of that area because of radiation. I think a government would use other means to stop riots.

other countries would most likely step in or impose sanctions

Either

a) The riots wouldn't end, or

b) The country would end, because everyone would be dead.

Everyone in the country would die.