There is undoubtedly a ton of socialist history regarding the promulgation and study of Esperanto.
https://en.prolewiki.org/wiki/Esperanto
It does not seem like it is nearly as popular as it once was, but there are examples of it being used and even celebrated in Cuba, China, and the DPRK.
I adore the idea of a lingua universalis. I am also aware of many of the criticisms of Esperanto, from its ostensible Eurocentricity to its difficulty with escaping unnecessarily gendered language.
Is there much use in learning it, outside of personal interest or as a hobby? Do you think that there are Esperantist movements large enough to justify learning it? Enough speakers?
Iirc, back when I was interested in learning Esperanto, one of the criticisms I saw was that it’s very Eurocentric in its design. It strives to be a “universal language” but is very obviously rooted in Romance language. However, conversely, I remember seeing the argument that learning Esperanto for a second language is comparable to learning the recorder for music: it’s not so much that you will use the skill in Esperanto, but more you will use the skill in language-learning to more easily learn other languages.
Personally, I think Esperanto is pretty neat, especially conceptually, but probably not too practical unless you’re involved in the Esperanto movement and committed to it. I believe there are people raised to speak it natively, and there is a sizable international community. It could still catch on, given the right spotlight.
Globasa looks like neat alternative “universal language” project that’s doing a least a little better than others at avoiding eurocentrism. Every world language family has to be represented.
Looking at a few of the sample sentences I see of the language, it would be a great language to use in a fictional setting. Just gotta swap out the characters. And honestly, using it in a good work of fiction would help its popularity immensely. Just look at the number of people who study Klingon or Elvish.