What does enableNametagScreenBuffering in Exordium options mean?

It basically renders the nametags only x times per second. Ofc this causes some stuttering of the nametags when moving the camera, so it's disabled by default. Probably primarily interesting for game server lobbies like Hypixel or Cubecraft.

Also why the translation key, it should show up with the correct name "Enable Nametag Buffering"?

yes, it did, but I still did not know what it meant.
anyway, thanks for the clarification!