Hi AmigaKit 
Is it really no problem to change UK keyboard <-> DE keyboard?
Just a question: What, if i have a british A1200 and use a german keyboard -
can I use german keys like ö, ä, ü, etc. after changing UK -> DE keyboard in
WordWorth, FinalWriter, etc.?
Yes they use same keyboard interface. Actual keys are defined by keymap and you can use umlauts if you switch to DE keymap. You can change keymap from locale settings (SYS:Prefs/Locale).
You could also use UK keymap with DE keyboard. Just some keys are in different places.