A lot of different languages are available for the Back-end, but by default this language may not be installed. If you want a translated Back-end, get your language pack and install it using the Extension Installer. After this, go to the Extensions Menu, select Language Manager and make your language the default one. Your Back-end will be translated immediately.
Users who have access rights to the Back-end may choose the language they prefer in their Personal Details parameters. This is of also true for the Front-end language.
A good place to find where to download your languages and localised versions of Joomla! is Translations for Joomla! on JED.
Jacques Gandini vous reçoit dans sa maison originale et confortable de la médina de Ouarzazate.