I read some XFree READMEs. They are talking about a possibility to configure keyboard layout 'backward compatible' - but I could not find out how (it might help).
You don't need to. you can tell your X to use us,de as the keyboard, but to always be in grp2. Actually, what I just said counts as "backwards compatible", as that is what happens on 4.2.x. Does anyone know, off the top of their head, how to do that?
I tried to cheat wine with "us,de" together with ",nodeadkeys" and "grp:ctrls_toggle" (toggle between us and de with pressing both ctrl keys). Doing so resulted in a screwed keyboard, e.g. a-z keys now had special meanings in KDE, running wine did not give me access to '{[]}' keys. KDE itself has been screwed (maybe since I pressed lots of keys for testing while they had special meaning).
I made tests with several different toggle keys and configurations, but no success... meybe there is no easy solution.
Regards, Tim