And since NWN2 is on my brain; I’m pretty sure one of the KC’s first languages is Elven. Like two examples; There’s a statue in the Temple of Seasons with an elvish inscription written into it which the KC can read. Secondly, if you get the spider Kistrel but don’t have Sand or Elanee with you, when Kistrel signs their name in elven runes the KC can read it themselves.
Neither of these have lore or race checks, meaning that the KC is fluent regardless. So it seems like maybe Daeghun raised them speaking elven, and he and the KC speak in elven when they talk to each other (rare as those occasions may be)