Regarding the "code": I'm pretty confident that the FBI is not the inventor of it, so obviously there should be some information out there about "encoding a me

Regarding the "code": I'm pretty confident that the FBI is not the inventor of it, so obviously there should be some information out there about "encoding a message to that the encoded message is human language". Obviously there's a mapping (assuming x,y are unknowns) (x | "through good ole Unk") -> "by skyjacking a jet plane". (y | "And please tell the lackey cops") -> "I am 1st Lt. Robert Rackstraw," Doesn anyone know candidates for this type of mapping?