SUMMARY

If the different input languages are set up in the Plasma desktop, it's sometimes impossible to open a plasmoid (e.g., Network Manager) from the tray.

STEPS TO REPRODUCE
1. Add at least two input languages via the System Settings. In my case, they are US English and Russian.
2. As well, in the System Settings choose the "Application" Switching Policy.
3. Click on the desktop or open the Plasma main menu and ensure that the default input language is selected for the Plasma "itself".
4. Open/activate any widow and switch to the input language being non-default on your system. E.g., on my system US English is the default input language; so, in such a case, it's needed to switch to Russian while the selected application's window is active to reproduce the bug.
5. Click on a plasmoid's icon on the tray. E.g., chose the Network Manager icon, but it doesn't matter -- it may be the Audio Volume plasmoid.

OBSERVED RESULT
After some time of working, the Plasma enters in a state when the selected plasmoid can't be opened if the active window's input language doesn't match to one of the Plasma desktop "itself". Instead, I observe something like a placeholder semi-transparent rectangle surrounded with a shadow, which even appears with an animation, but immediately disappears. For the short time while the plasmoid "tries" to appear, the language indicator on the tray is being switched to the default input language, but immediately being switched back to the language chosen for the active window.

EXPECTED RESULT
It's should be possible to open the plasmoids nevertheless which language combination is currently selected.

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: Arch Linux
(available in About System)
KDE Plasma Version: 6.0.4
KDE Frameworks Version: 6.1.0
Qt Version: 6.7.0
Graphics Platform: X11 21.1.13

ADDITIONAL INFORMATION
1. I faced with this behaviour after switching to the Plasma 6. On the Plasma 5 I never observed this.
2. It looks, the Plasma reaches this state after several hibernate-restore cycles. But, probably, there is possible to reproduce this bug after long time of working without the hibernate.
3. If switch the input language for the window from my bug's description so that it matches to the default (i.e., chosen currently for the Plasma desktop "itself"), it's becomes possible to open the plasmoids. As well, if the Plasma desktop's input language will be switched to be matched to the active window's one, the plasmoids can be opened too. I.e., I found that the plasmoids can't be opened IF the input languages don't match between the currently selected window and the Plasma desktop.
4. I fond no other preconditions to achieve this buggy behaviour other than the long (day or two) working with the Plasma and/or several hibernate-restore cycles.
5. Apart from the long reproducing time, on my system this bug is being reproduced always after some time of working in a session because I always use the hibernating to store the working environment.
6. If the Plasma reached that state, there is no ways found (by me) to workaround this behaviour other than the reboot.