Hi,
mimas has been very kind and produced a script to change the locales, based on the files in $HOME/.config/openbox/lang.
I have tested and integrated this to a new archive which you can get here:
http://meets.free.fr/Downloads/debian/configurations/openbox-language_switcher.tar.xz (http://meets.free.fr/Downloads/debian/configurations/openbox-language_switcher.tar.xz)
here is what it looks like:
(http://meets.free.fr/Downloads/debian/images/language-switch-en.png) (http://meets.free.fr/Downloads/debian/images/language-switch-fr.png)
(http://meets.free.fr/Downloads/debian/images/language-switch-de.png)