OK, I've come a bit closer to a solution AND I have slept a night after becoming all frustrated from trying to get things to work.
first, I will properly explain my setup:
I've edited /etc/inittab to "create" a new runlevel 5. It basically is configured like runlevel 4, only it calls rc.5 instead of rc.4.
rc.5 is (edited from rc.4):
# rc.5 This file is executed by init(8) when the system is being
# initialized for run level 5 (XDM)
# Version: @(#)/etc/rc.d/rc.5 0.00 09/07/08
# version date is 9 july, I'm Belgian!!
# Author: Fred N. van Kempen, <firstname.lastname@example.org>
# At least 47% rewritten by: Patrick J. Volkerding <email@example.com>
# Rewritten by Jan Herrygers for starting an x session instead of xdm
# Tell the viewers what's going to happen...
echo "Starting up X11 session..."
# start a login session for user username
if [ -x /usr/bin/startx ]; then
exec /bin/su - username -c /usr/bin/startx
# extra optie, als er iets misgaat met startx
# If all you have is XDM, I guess it will have to do:
if [ -x /usr/bin/xdm ]; then
exec /usr/bin/xdm -nodaemon
elif [ -x /usr/X11R6/bin/xdm ]; then
exec /usr/X11R6/bin/xdm -nodaemon
echo "Hey, you don't have startx or XDM. Can't use runlevel 5 without"
echo "one of those installed."
# All done.
Now, when I'm in runlevel 3, and I log in as the normal user (lets call the user "username") and run startx, xfce comes up in Dutch. When I switch to runlevel 5, xfce comes up in English.
when I'm in runlevel 3, 'echo $LANG' returns nl_BE@euro
in runlevel 5, it returns a blank line
Long story short: It seems like the environment isn't set up correctly the way I initiate startx.
Question: how do get it to do what I want?