XFCE & setxkbmap
 

The keyboard seems stuck on en_US in xfce 4 - you can't set the LANG variable to en_GB in Settings > Window Manager. If I open Konquerer, then change the kb from settings://Regional and Accessibility, it works, but only as long as Konquerer is open. I tried copying the command it showedinto a terminal, but no luck.

You can specify keyboard options at /etc/X11/xorg.conf.
Also if you want to set globally the LANG variable edit it in /etc/profile.d/lang.sh

Editing /etc/profile.d/lang.sh looks like it might be the answer. Thanks!
The kb was already set in xorg.conf and working at the command line, which is why I was so confused. Now all I have to do is restart the daemon that executes lang.sh (I'm assuming that the "d" stands for "daemon"). Er... how do you do that? :o

Well, it happens that profile.d is not a daemon :)
The scripts inside profile.d are executed by /etc/profile which is read everytime you login into some virtual terminal (or a some X term with login activated).
I would suggest you to quit X, logout, relogin, and start X again.