The Secret Language question

Looking for a specific book with a made up language, the kids in the books used it to talk/write letters among themselves, the entire book was not written in this language. I can not recall the title or the author of the book. the language went something like this (I think)

Ooking-ling or-fong a-ang ecifi-speng ook-bong ith-wing a-ang ade-ang anguage-lang

Anyone that can help?