Books with Secret Languages

My third novel,Symbiosis(Publication Date: 21st January 2016), is about identical twin girls called Talulah and Taliah. It is a psychological thriller. Talulah and Taliah speak to each other in a cryptophasia. A cryptophasia is a secret language developed by a set of twins, which only they understand. The word originates from the Latin crypto meaning secret and phasia meaning speech.Symbiosisis the first ever work of fiction to incorporate a cryptophasia.

Here are 6 authors who invented/allu...