The sticker referred to is not an international drivers license. It is a tax sticker that is necessary to drive on the autobahns in Austria and Switzerland. In one of these countries, they are generally purchased for one month periods and the other annually. If you rent a car near one of these countries or in one of these countries, there is often already one attached to the windshield bought by a previous renter that is still valid. In that case you do not need to buy another one. If you have the bad luck to rent a car without one already there, just buy one as you cross the border. In either country, you can drive the non-autobahns without the sticker. The stickers are not that expensive, but I don't recall the cost.
Every time I have driven in Austria or Switzerland, I rented the car in Germany, and except on one occaision, I have had a valid sticker for at least one of these countries, and on a couple of occaisions, both, already on the car. If you don't have one, stop at the first turnoff after crossing the border, and if there is not a sign, ask where you get one.
As to an international drivers license, I had one once and did not see any need to ever renew it or get another. There may be some place that it is necessary or useful, but I have yet to find it!