On a strange island inhabited by demons and spirits, a man battles the forces of evil!
Esperanto is a constructed auxiliary language devised by Polish ophthalmologist and linguist L.L. Zamenhof in 1887 to foster harmony between people from different countries. The vocabulary stems mostly from the Romance/Latin languages with additional input from Germanic, Slavic, and Greek languages.
Who knew that it would be used to make a film? And a film that stars a pre-Star Trek William Shatner. The idea was that use of Esperanto was intended to create an eerie, other-worldly feeling and makers claimed they hoped for greater international sales.
It was thought lost forever when the negatives were destroyed, but a single copy was found in 1996 in Paris and used to create all current videos of it. Give it a watch or read more about it here: https://en.wikipedia.org/wiki/Incubus_(1966_film)