Some background: When I moved to Germany in 2012, I traded in my Wisconsin driver's license for a German one. I was told, if I ever move back, I can just go back into the office and trade my German license for my American license. I know that my Wisconsin license number is on the back of the German license. My Wisconsin driver's license expires early next year, on my birthday.
My question: do I need to renew my Wisconsin drivers license to keep my German license valid? If I let the Wisconsin license expire without renewal, will there be any problems for me in Germany?