The language section lets you manage the languages available for the store front. Cart provides English as the default language after installation. To add multiple languages to the site you need to install a language pack. Language packs can be acquired from the Extension Directory. See Adding multiple languages to learn how to add a language pack to Cart.
If the new language pack is already installed into Cart store, the new language can be added to the site under System -> Localisation -> Languages. Press the Add button on the top right corner to add a new language. The following information will be needed to fill.