This question discusses driving in a specific country (Austria), but it raised a point I did not realize: some countries require an International Drivers Permit (IDP) to drive. I was always under the impression that it was optional if your license was in English or another widely-spoken European language. In other words, your issuing country determines if you need one, rather than your travel destination.
I looked at the dmv.org web site, but I couldn't find a list of countries that require this. They recommend getting one for driving in any foreign country (but that's not surprising, considering that's their business...)
Is there a list somewhere of countries that require an IDP for some drivers?