I use the last Kubuntu 15.04 from site and while installation choose to upgrade. I have several layouts: English, Russian and Swedish. The key for layout changing is the Left Win. Several minutes it worked, but then I can't change the layout: key doesn't work and changing the layout in the tray also doesn't work. As a solution I use. Then I go to settings, undef layout key, click apply. Then define layout key, click apply - language switching begins to work. Reproducible: Always
KDE 5.09
or 5.9
KDE 5.9.0 - correct=)
I have the same issue with Kubuntu 15.10 / KDE 5.4.2
Just to add an other data point: The issue still reproducible on KDE 5.14 (arch linux). If I change the layout with the widget on tray, the keybinding will start working for a time, but it soon stops working again. Because of this bug, I've tried to switch to Cinnamon (4.0.9), but interestingly that has almost the same issue. The only difference is, that on Cinnamon, the keyboard layout switching applet disappears from the tray the same time when the keybinding stops working. Changing the keybinding in the keyboard settings app re-enables the applet and the keybinding for a time. Could it be a common dependency, or copy/pasted code?
There's good chance there's something on your system that resets keyboard layouts. Usually it's input method daemons, try disabling input method on your system and see if it helps.
(In reply to Andriy Rysin from comment #6) You were right, my issue is unrelated. Running `setxkbmap -print -verbose 10` told me, that the initial "us,hu" layout has been changed to "us", and this is the reason for the disappearing layout selector widget.
Sounds like this was caused by somebody else's code interfering with it.