While non-cannon (with the writing of the prequels), from The Dune Encyclopedia ... > The earliest history of the native inhabitants of Arrakis indicates that

While non-cannon (with the writing of the prequels), from The Dune Encyclopedia ... > The earliest history of the native inhabitants of Arrakis indicates that they were the sole remnant of a people known as the Zensunni Wanderers, originally followers of a "prophet" named Maometh, circa 1381 E.G. The Fremen broke away from the main sect to establish their own religion based on an ultraconservative notion of living life according to "the ways of the fathers." Given the Fremen's roots in such a religion and the particularly life- threatening environment that Arrakis afforded them, the Fremen developed a set of cultural institutions unique in their perfect balance between the philosophical world view demanded by imposed Fremen faith and the harsh reality imposed by Arrakis's nature. These institutions remained stable for thousands of years and are significantly changed by only two events. The first was the arrival of Pardot Kynes as the first planetologist of Arrakis. The second was the transfer of the governance of Arrakis from the House Harkonnen to House Atreides in 10190 and the subsequent emergence of Paul Atreides as Paul Maud'Dib. Kynes expanded the cultures of the Fremen to include the hope for a second flowering of Arrakis; Paul Maud'Dib forever changed that culture, thus, for all intents, the ancient culture of the Fremen ceased with his rise to power. And an example from first page of the section on Fremen Language: https://i.imgur.com/jiRQNVv.png https://i.imgur.com/jiRQNVv.png and a bit from the history of the language: https://i.imgur.com/QQq5gfO.png https://i.imgur.com/QQq5gfO.png