LC_ALL must be empty - it is a troubleshooting and bug finding variable which should only be set prior to executing a terminal command e.g.
LC_ALL=C; some-command
KDE is a pain when it comes to locale - because KDE stores a subset of locale settings in obscure *rc files.
Also remember that - any script can change the locale when needed or just for the fun of the user pulling hair - the latter is probably rare - but it was fun to write.