In order to activate a language in eFront, log in as an administrator, and from your Administration dashboard navigate to languages. 

Here you will be able to view all available languages in a tabular list.

To activate a language use the toggle operation to activate it (1). Inactive languages will appear in the list with red color.

Once you have activated a language it will be available in your language options (2) for the user languages or the system default language.