Actually, La Guerre des Etoiles is a pretty decent translation. Les Guerres de l'Etoile makes it sound like they're fighting over a single star.
'Star' in Star Wars is an adjective so the title describes battle AMONG the stars or in outerspace, not battles FOR a star.
A more authentic translation would be Les Guerres Stellaires.
But I find that there are one too many "ère" sounds and doesn't quite have the same vocal lyricism of La Guerre des Etoiles.