August 14 is Navajo Code Talkers Day commemorating the date in 1945 when Japan unconditionally surrendered (although the signing did not take place until September 2.)
The use of rare languages as a cryptology was intermittently used during both WWI and WWII and included Basque-speakers from Spain, Wenzhou-speakers from China, Welsh-speakers from the United Kingdom, and Nubian-speakers from Egypt.
However the use of Native American languages in WWII was by far the most widely and effectively used. The languages included Assiniboine, Cherokee, Choctaw, Hopi, Meskwaki, Comanche and most prominently Navajo.
The Navajo code talkers were commended for their skill, speed, and accuracy demonstrated throughout the war. At the Battle of Iwo Jima six Navajo code talkers worked around the clock during the first two days of the battle. These six sent and received over 800 messages, all without error, and they are responsible for advancing the close of WWII.