To be more specific, (before reverting fcitx-qt5) I was totally unable to switch the input mode from English to Japanese, either through the previously set up key binding or through the graphical interface. The panel icon for the Japanese input method (mozc) was still displayed in the panel. In fact the mozc icon was permanently displayed even when typing in English. (Usually, when switching to English input mode, the mozc icon disappears.)
I ran the following command to check for errors:
which produced about 100 lines of output, none of which gave me any idea about the nature of the problem. There is one crash.log in
~/.config/fcitx/log/ with the following content:
fcitx: BadWindow (invalid Window parameter)
but this log was created before the problem occurred.
I did search for upstream bug reports, but I couldn’t find anything relating to the issue I was having. I’ve tried searching “fcitx bug” and “fcitx-qt bug” (filtering for items posted in the last month). I have also been to bugreports.qt.io and searched “fcitx”.
I thought I would try reverting fcitx, just to check whether the upgrade was really the cause of the problem. When I looked at the packages in
/var/cache/pacman/pkg/, I selected fcitx-qt by chance (instead of fcitx itself) for reversion, and it worked.