my Chinese input via ibus does only work, if I remove all fcitx packages. But every time I update the system it wants to reinstall everything. How can I configure that my Chinese input works (either with ibus or fcitx)? I don’t really care which one I use, just want it configured so that it works without me having to remove packages all the time.
I have no idea about the root cause of your problem, but when you do not want that some packages (fcitx ones in this case) are installed on every update action, the taboo them.
Search them with YaST > Software / Software installation, right-click on the package and choose Taboo.
fcitx integration is far better in openSUSE / Plasma than IBUS (IMO).
If you remove ibus does that also get reinstalled on system updates? I don’t see the issue here in Leap 42.3 . . . and indeed having both installed wouldn’t stop the other from working.