And i think you shouldn't. Different characters should speak in a different way, i think it's called poliphony, technically As long as the narration has a consistent style character should espress themselves through their speaking registries too.
Time ago i read The First Law trilogy by Abercombie, which is a good reading indeed, but he literally used a completely different registry for each pov chapter on the base of which character the chapter focused on. Cool, but insane

Kinda tiresome on the long run.