Book: The 5-Minute Linguist
Chapter: 17. What Ever Happened to Esperanto?
The only proposal of an international language that had lasting success was Esperanto, invented in Poland in the late nineteenth century by Ludwig Zamenhof. It was created in 1887, got a boost in popularity in the 1920s and even became a candidate to be the official language of the League of Nations. Esperanto is by far the most successful language in the long history of language invention. It isn’t a universal language, and it’s unlikely to become one, but it has become a living language.