So, Germany and Austria both have programs where if you are living in a country for more than six months to a year, you can file some paperwork, get some translations, and have an eye exam, and then they will issue you a driver's license in exchange for your valid US license (depending on the state, sometimes). But what happens if you then go back to the US and want to rent a car? Or move permanently back? Will any US states exchange the license back? Can I, as a US Citizen, drive in California at all if I have a German (or Austrian) driver's license plus IDL, or is it only valid for foreign citizens?