translate.google.com shows a German keyboard with y and z transposed, the umlauts and so forth. not only can one mouseclick the keys on the screen keyboard, the amazing thing is that my REAL KEYBOARD is transformed so I can easily type umlauts, much easier than the Duolingo system.
I use that all the time. worse thing is to do ctr+Z ;), but works fine for me.
We accept ue for ü. If you're on a mac there's a very helpful shortcut: option+u, then a/o/u and you get the umlaut. Let me know if these shortcuts help you!
also on a MAC, you can just enable a german keyboard input, and then your keyboard behaves like a german one. (SystemPref->Keyboard->inputSources). Swtiching between English/German is then using cmd-space. However, replacing "z" with "y" broke me eventually and I started using the option-u for umlaut, option-s for eszett.