KDE keyboard repeat delay/rate settings don't work/have no effect?
In the Startup and Shutdown → Background Services configuration applet,
make sure the Keyboard Daemon service ("Enables switching keyboard layout through shortcuts or system tray") is checked and in the "Running" state:
If this does not seem to have an effect, log out and back in. The settings should be applied afterwards.
For whatever reason this service is also responsible for propagating rate/delay changes to X11, which you can see live via:
watch -n1 'xset q | grep "auto repeat delay"'