Esperanto's success is really astonishing. Esperanto is widely spoken around the world, and has continued to gain new speakers and even many native speakers for over a century. No constructed language can boast anything like that. (IIRC it is widely spoken in China as an alternative to English.)
Esperanto is only considered a "failure" in terms of its original goal of becoming the second language of every educated person in the world. Not even any natural language, even such a powerful one as English, has ever achieved anything so ambitious.
> Esperanto's success is really astonishing. Esperanto is widely spoken around the world, and has continued to gain new speakers and even many native speakers for over a century. No constructed language can boast anything like that.
What evidence do you have the the number of Esperanto speakers are increasing? The best source I could find
thinks that this question is very difficult to answer: Depending on the data that one considers the number of Esperanto speaker can be increasing or decreasing (first diagram hints at a strongly decreasing number since about 1990, second at an slowly, but steadily increasing number).
One reason is that many 20th-century totalitarian regimes had a problem with Esperanto: https://en.wikipedia.org/wiki/Esperanto#Responses_of_20th-ce... lists Nazi Germany, Francoist Spain, Soviet Union and Imperial Japan.