In the late 1960's and 70's, there was a lot of interest in Esperanto. I haven't seen it mentioned again until recently--I assumed it went the way of making furniture out of the weeds in the backyard, and other groovy 60's stuff. Esperanto was, or is, an invented language--it sounds like a bastardized version of Spanish. The man who invented it, in the late 19th century, had the idea that if everyone studied it, people all over the world could talk to one another. The idea sounds very reasonable, but most of the people interested in it seemed to have a somewhat tenuous grasp of reality. Esperanto was supposed to be so simple that it could be learned in a matter of weeks. The main problem was that the only people an Eperanto-speaker could speak to were the other Esperanto-speakers from the Esperanto class. The Esperanto speakers might have done better learning a pidgin language. A pidgin language develops out of necessity, taking and using any words or phrases it needs to communicate effectively, and ignoring everything else. People who work on the merchant ships speak a pidgin of only several hundred words, and manage to work together at varied and complex tasks.
Although it never became a useful language, Esperanto would make a good research subject. Through study of Esperanto we might learn why people so often ignore invented or synthetic symbols and words, while taking up words and phrases that develop organically.