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?
No. Even in the countries you mentioned, there are not enough speakers to justify learning the language to communicate. You’d be better off learning Spanish, Mandarin, and Korean respectively.