I can't see how $LANG, or /etc/sysconfig/i18n is supposed to be set on a KDE system.
The 'system settings' control panel has 'Personal -> Keyboard Layout' but that applies to X apps once the user has logged in to X, not the system, and provides a way of the user changing the keyboard at runtime. It's 'disabled' on mine because I never need to change the keyboard.
A Google search suggests running 'system-config-language'. This I did, it installed some en_GB rpm using PackageKit and edited /etc/sysconfig/i18n.
Someone opting for a KDE setup will not get directed to run that config as it's not part of 'system settings'.
As an aside, Anaconda put 'LANG=en_US.UTF-8' in my grub.conf. I changed this but it had no effect.