In Germany, people cannot renew their borrowed books in libraries?Is it true?

Sometimes people in an organization do not understand their own rules. You will experience that everywhere, not just in a German Library. There is a reason that person is a grunt in a library and not running a successful business. Just return the CD and then when they have it checked back in take it out again. If you can, request it online as soon as you have returned it. In my library, that means that they will have to pull it for you and have it waiting at the front desk for you!