(Credit: Bernd Uhlig) The Deutsche Oper Berlin’s current “Nabucco” is a production by Keith Warner, first presented in 2013. It’s not an unconventional production, at least by Berlin standards. Where Berlin opera is often characterized by the most provocative nontraditional productions—Frank Castorf’s recent “Forza” premiere, for instance, provoked a near-riot among its Deutsche Oper audiences—Warner’s “Nabucco,” by contrast, feels tame. {…}