Thailand signed up the international agreement for international driving licenses and as long as you use it in conjunction with a driving license for your country of origin
But the Thai police seem to enjoy ignoring this and hand out fines willy nilly
Thai people can legally drive a car most countries as long as they have there driving license and the thai equivilant to the international driving permit
I believe the permit is valid for 6 or 12 months cant remember which. And there are different permits for different parts of the world