RPG Museum

Talking like a normal person is the principle that it is acceptable to speak in a conversational and unembellished way while playing or GMing. Neither in-character voices nor narrative description need to be overly elaborate or fanciful. The principle both encourages players to play without worrying about their vocabulary and acknowledges that the play examples in many role-playing games don't always reflect the casual styles actually used when those games are played.

The game Heart by Grant Howitt includes GM advice for talking like a normal person, including the following (replicated with permission):

For some reason, many roleplaying games seem to think that everyone talks like the narrator in a fantasy novel. Examples of play have the GM saying stuff like: "As you enter the ominous chamber, scintillating light plays across your worn armour, and the priest says: 'Prithee sires, welcome to this, the most humble temple of her Subterranean Grace!'" This is a lie. Pretty much everyone sounds like "Okay so: you, uh, you walk into the place. And it's spooky, and there's sort of like - shining lights in there? It's sharp, like a crisp line between light and shadow. Anyway there's a guy in there - a priest, weird lookin' guy - and he says: 'Hello! Come on in to the temple!'" It's okay to use a conversational tone.[1]