Language loss is knowledge loss and irrecoverable.

Uldarico Matapí Yucuna, 63, is often called the last #shaman of the Matapi, an Indigenous group of fewer than 70 people living along the Mirití-Paraná River in the Colombian #Amazon rainforest. His father was a shaman and taught him ancestral knowledge, including how to use plants to treat all kinds of maladies. But Uldarico rejects the title because instead of living with his people, for the past 30 years he has been in Bogotá documenting in writing what is left of this knowledge.

https://www.science.org/content/article/medicinal-knowledge-vanishes-indigenous-languages-die