Spoken Language.

Have a way to set a default language for each creature. Also have a way to override it when doing a say/whisper/yell. Have the message be displayed as says [in goblin]. Also make it so if a player does not have a language in their skills it will just be "says something in a language you don't understand".

This isn't a real high priority for me though. There are other things you are working on that is way more important to me, like dynamic fog of war and a better spell system.