body: So, if it's either such an esoteric language that only the signatories speak it (say, a new variant of Esperanto, or an idioticon between twins)? Or if it were an archaic language- say, the two foremost professors of classical language in the world sign a contract written in a language which people technically know about, and can become experts in, but which essentially no one else has devoted the time and energy necessary to become expert in?
  
  
  (I ask because it is Friday in Iceland.)
  
  
  
title: Is a contract valid if it's in a language only the signatories speak?