It's called Las Noches ( The nights) because it's always night that's why Aizen used a fake sky and daylight.Also it must be some japanese thing, sometimes japanese are fans of mexican culture. The name of the atacks and some characters come from spanish. Arrancar= ripp off , Espada=sword/blade
Hueco mundo=empty world , menos grande= less big-or smallest( maybe the intention was to call them mas grande-biggest-more big) El directo= the direct (punch) ,Brazo del diablo=devil's arm
etc.