The best way to imlement adding language to multilanguage database is to create a language reference from a existing language reference.
In my sample below, I get the language rerefences of language with id 3 and clone it into language reference with language_id 4.
INSERT INTO gallery_pictures_l (languages_id, picture_id, description)
SELECT 4, picture_id, description
FROM gallery_pictures_l WHERE gallery_pictures_l.languages_id = 3;