This has not been my experience and only a handful of European countries require an international driver's license/permit, so long as your home country Driver's License is issued in Roman Characters (e.g. no Arabic, Cyrillic....etc).usually European rental car agencies ask to see it. We always get an updated one before we leave.
European countries that officially require it, include: Austria, Bulgaria, Czech Republic, Estonia, Greece, Hungary, Italy, Poland, Romania, Slovenia, Slovakia, and Spain. However, I have rented in Austria, Greece, Italy and Spain with my US license and not been asked for an international driver's license. As always, your experience may vary, but outside the above list I would not bother getting one.