The literal translation of "se la", whether French or Spanish leaves a void in meaning obviously, unless it's an abbreviation of "se la vie". I'd love to ask Lionel what really as up with this, but if it's a "shorthand" of "Selah", that really fits the spirit of what he's getting at in the lyrics, I feel. Just as in John Lennon's "Imagine", if we do what "Selah" conveys and stop, think and reflect of what the world could improve to-well then we're cookin!