I solved it like this, use another password. I am on a Mac so I enabled US layout in addition to the Swedish one I normally use. Then I typed my password in a text editor. Now do the same thing with US layout. If there is a difference, then you will have problems like not being able to unlock filevault2 on a mac with your yubikey. And because you only can use US layout in the yubikey personalization tool you have to use a password that does not differ with layouts. It's really not yubico:s fault, it's just how things work in general. Well unless you're an american of course.
So when you have one that has the same characters for german and US layout you have a winner. (This does however lower the security quite a bit if you are not thoughtful of how you do this).
Good luck