My understanding of the law relating to the IDP is slightly different. The IDP doesn't "let you drive in other countries" ... it's a convenience if you are driving in a country that uses another language. The IDP is supposed to provide a multilingual translation of the information that should be on your official drivers license (hair color, height, required to wear glasses, etc.), so that if you're pulled over, you don't have to wait in jail while the local cops take their time finding a missionary to translate your home driver license.
But the IDP is supposed to come from the same country that issued your official drivers license; in the US the State Dept has authorized just two organizations, the AAA and the National Touring Assn, to issue IDPs, for $10 or thereabouts ... and they insist on taking the data off your real drivers license. The IDP doesn't work if it's not in tandem with your real drivers license. And in the US, at least, if you show cops a drivers license in one name and an IDP in another name, you can expect your travel plans to be seriously disrupted. Contrary to the claims made by the internet con men - who are mostly peddling wildly overpriced IDPs issued by third world travel agencies (and sometimes not even genuine IDPs but counterfeits) - an IDP does not make you immune to traffic laws, does not make you immune to arrest, does not work in the absence of a real drivers license, etc.