and I cannot preserve my system keyboard settings - they revert to English (US) after every reboot after editing
YaST->System->Language and YaST->Hardware->System Keyboard Layout (it was set to UK already, so I set it to something else first).
# Local users will get RC_LANG as their default language, i.e. the
# environment variable $LANG . $LANG is the default of all $LC_*-variables,
# as long as $LC_ALL is not set, which overrides all $LC_-variables.
# Root uses this variable only if ROOT_USES_LANG is set to "yes".
# Keyboard mapping
# e.g. KEYTABLE="de-latin1-nodeadkeys", "us" or empty for US settings
.kde4 is not where current or recent versions of Plasma store much of anything. Plasma5 settings are mostly in ~/.config/, mixed up with many other personal settings. Your problem suggests to me a permissions problem in your homedir. If you login as a new user, is the trouble the same?