The Nacaal language is a fictional language system which was first suggested by Mayan scholar Augustus Le Plongeon. H.P. Lovecraft used the Nacaal language in a number of his stories, most notably Out of Aeons.
The Naacal language and its script were used by the early human inhabitants of the continent of Mu over 173,000 years ago. The letters are slightly similar in appearance to certain mesoamerican language systems. Some scholars have suggested that occasional similarities between Naacal and Mayan script are not coincidental. The occultist Harley Warren was supposedly an expert in deciphering and reading Naacal script.
The most notable examples are the Zanthu Tablets stored in the vaults of the Sanborne Institute for Pacific Studies and Captain Abner Exekiel Hoag's original palm leaf version of the Ponape Scripture. The Cabot Museum in Boston held a peculiar scroll which may be written in Naacal though it has vanished from the public eye after the 1932 scandal.
The Unaussprechlichen Kulten contains a key to deciphering Nacaal script and a rudimentary dictionary of Naacal phrases. Colonel James Churchward planned to release a monograph on prehuman languages called the Nacaal Key but it is unknown if it was ever published.
Harley Warren and Randolph Carter studied a book written in Nacaal that they received from India. This book revealed the location of an ancient tomb and a way to get to some evil legion of things beneath the tomb. Warren disappeared with the book underground and Carter lost all memory of the book and its contents. Naacal is also compared to R'lythian by Carter while explaining his own later disappearance to Etienne-Laurent de Marigny, Ward Phillips and Ernest B. Aspinwall.