There is no such thing as an 'international drivers license'- there are a pretty comprehensive series of treaties where countries recognize each others' drivers license credentials as valid for non-resident short term use (typically 3-6 months).
There is something called an 'International Driving Permit', which is a translation of your existing driver's license and not an actual license itself. Some countries like Austria technically require an IDP though it's unlikely you'll be asked for one. (When the German rental car clerk heard we were planning on driving in Austria, all he cared about was whether we understood the toll road sticker system) and it's a good idea in general if you're driving in a place where the alphabet is different than the one on your driver's license. The only legal seller of an IDP in the USA is your local AAA office, and it will cost you $20 and two passport photos.
International Driving Permits