(From Atlas Obscura. Link to the complete article given below)

A chain of mountains splits the center of Papua New Guinea, crossing east to west for nearly a thousand miles. These highlands are full of peaks and V-shaped valleys, covered in forest and hard to reach—a terrain that has isolated clans for millennia, leading to the country’s famously diverse languages and cultures.

On these mountains grow the pandanus tree, up to 90 feet tall and bearing clusters of knobbly, pineapple-like fruits; eaten raw or cooked, they taste a little like pecans. This dense, high-fat nut is preserved during famine, smashed into pudding, consumed during ceremonies, and connected to the earliest signs of humanity in Papua New Guinea. As far back as the Ice Age, residents were leaving the coasts to trek into the mountains to harvest them. Over time, the harvesting expeditions took on ritual significance, and spurred the development of a hidden form of language.

On pandanus-gathering expeditions, ordinary words cannot be spoken. Instead, people use pandanus talk. It is not a language of its own like Russian or Mandarin, but a style of language used in a special context, or what linguists call a “register.” Across Papua New Guinea, different clans with different languages all switch up their speech when they gather pandanus, lest they risk harming the harvest.

Back when Karl Franklin lived near Mount Giluwe, the second-highest mountain in Papua New Guinea, the surrounding area was believed to be inhabited by wild dogs. Franklin, a now-retired American linguist, first traveled to Papua New Guinea in 1958 to help catalog the local languages. He and his wife lived in a village with the Kewa people, five hours from the nearest government station. Franklin would spend the next few decades creating an alphabet for Kewa (then solely an oral language) and, eventually, compiling a dictionary.

Read more at this Atlas Obscura link