How add a new languaje in my Jahia Portal 5.0?

[Jaime González de Zarate]

Hello I want to know how add another languaje wich is not included in 
the list of already configured languages of
the administration area. Does anyone have an idea how solve this problem 
and could me a hint?

In the Web http://ftp.ics.uci.edu/pub/ietf/http/related/iso639.txt  it 
explains that cídogo for the Basque language is eu Basque. But I do not 
know what I must do. Could say the steps to me that I must follow?
Thanks in advance.
Jaime González de Zárate Fernández.