"Michael Engel"
Which method is easiest/recommended: 1) doing the install in English or German and add Japanese language support. 2) doing the install in Japanese.
In 8.1, I found 2) much easier. I think that 1) is supposed to be not much harder than 2), but for some reason when doing 1) I seemed to miss some settings that came automatically with 2).
Another question, if I do 2) can I later easily switch the menu and help texts to English/German ?
Yes it is easy, though you must do separate settings for the Linux base system and the KDE desktop. For the base system you will have to use YaST2 and input the superuser's password (unless you want to do the relevant editing manually, which would also need the superuser's password). For the KDE desktop, each individual user can set preferences in the KDE control panel. Using YaST2, I set LC_CYPE to ja_JP.eucJP, and might experiment with ja_JP.utf8 someday. This makes sure that Japanese input will be possible to terminal windows and every application that understands it. Other locale options can be set to English or German settings. In KDE, I set a list of languages to include both English and Japanese. KDE isn't very bright yet when it comes to a list containing more than one language. However, it didn't cause any crashes (yet) and it helped enable options in some of the free office applications to allow Japanese input.