"man bash" will explain the difference between .bashrc and .bash_profile. Most likely you want locale settings to apply system-wide, so you should set them in /etc/environment, then reboot. Plus, all prgrams started from the GUI inherit KDE's LANG et all settings, so you need to verify those as well.

PS: that's for a debian-style install. If you've got a beginner/knoppix install and a lang-XXX cheatcode active, I am not sure it will override /etc/environment