Complex sentence: Criminal laws can only address the future and not the past (criminal "ex post facto" laws are prohibited); and to be applicable, laws must be officially published in the "Journal Officiel de la République Française".
Split into simpler sentences: Criminal laws can only address the future and not the past (criminal "ex post facto" laws are prohibited). To be applicable, every law must be officially published in the "Journal Officiel de la République Française".