Got elementary OS installed at the local Neighbors House after shifting the original GPU, RAM and finally a defective motherboard. Yeah ':-p Will hopefully serve as a demo box for people around.
To achieve that I need to customize the Guest session, particularly the language, but am stuck half-way. Your ideas are welcome!
EDIT: screenshot of the partial (very incomplete) result with the settings below:
/etc/default/locale
LANG=fr_FR.UTF-8
LANGUAGE=fr_FR.UTF-8:en_US
LC_MESSAGES=POSIX
LC_PAPER=A4LC_TIME=fr_FR.UTF-8
$ locale
LANG=fr_FR.UTF-8
LANGUAGE=fr_FR
LC_CTYPE="fr_FR.UTF-8"
LC_NUMERIC=fr_FR.UTF-8
LC_TIME=fr_FR.UTF-8
LC_COLLATE="fr_FR.UTF-8"
LC_MONETARY=fr_FR.UTF-8
LC_MESSAGES=POSIX
LC_PAPER=fr_FR.UTF-8
LC_NAME=fr_FR.UTF-8
LC_ADDRESS=fr_FR.UTF-8
LC_TELEPHONE=fr_FR.UTF-8
LC_MEASUREMENT=fr_FR.UTF-8
LC_IDENTIFICATION=fr_FR.UTF-8
LC_ALL=
$ dpkg --list|grep language
ii language-pack-en 1:14.04+20150219 all translation updates for language English
ii language-pack-en-base 1:14.04+20150219 all translations for language English
ii language-pack-fr 1:14.04+20140707 all translation updates for language French
ii language-pack-fr-base 1:14.04+20140707 all translations for language French
ii language-pack-gnome-en 1:14.04+20150219 all GNOME translation updates for language English
ii language-pack-gnome-en-base 1:14.04+20150219 all GNOME translations for language English
ii language-pack-gnome-fr 1:14.04+20140707 all GNOME translation updates for language French
ii language-pack-gnome-fr-base 1:14.04+20140707 all GNOME translations for language French