1. Install locales
The first step is to install the languages you need
sudo apt-get install locales sudo dpkg-reconfigure locales
2. Optional: language packs
If you want e.g. libreoffice to use the new language, you'll need to install the corresponding language pack. Most programmes will NOT need this, but libreoffice and iceweasel do. The same goes for KDE.
sudo apt-get install libreoffice-l10n-fr iceweasel-l10n-fr icedove-l10n-fr
Basically, search for packages with l10n in their names.
Select the new language in GNOME 3 by gong to Region and Language:
Log out of GNOME and log back in again. Et voilà.
|And...we have French! French everywhere.|
4. Optional: set it in terminal
If you set the language in GNOME as shown above you shouldn't need to do this. However, if you are not using GNOME 3 you may want to set the language explicitly in your terminal by sticking the following in your ~/.profile or ~/.bashrc
When it's NOT OK:
|Note how it says 'Pays et Langue' but still says 'Activities' i.e. the language for some items has been changed, but not all.|