Xaczik
From Wookieepedia, the Star Wars wiki.
Xaczik was a language spoken by the Wookiees. It was one of rarer Wookiee languages with the primary one being Shyriiwook. It was mainly spoken on the Wartaki Islands and in other coastal regions.
While the Wookiees were enslaved by the Galactic Empire, the Wookiee resistance used Xaczik as a secret language to pass messages along. Since the Humans of the Empire thought all Wookiees were alike, they never realized that the Wookiees spoke languages other than Shyriiwook. Thanks to Imperial ignorance, Xaczik became an unbreakable code.
It was also used during the Second Galactic Civil War at Council Rock during the meeting there.
[edit] Behind the scenes
The use of Xaczik as an unbreakable code may be inspired by the American use of the Navajo language by codetalkers during World War II to send messages in the Pacific Theater without their being intercepted by the Japanese.
