*Disclaimer for any esperantistoj who see where this is going: I'm not a radical gender extremist, I swear! That being said, the ongoing discussion surrounding the way Esperanto handles gender is hard to ignore if it's a topic you think about a lot, so here's my tentative contribution.*
In case you're not aware, Esperanto is a constructed language created by Dr Ludwig Zamenhof in the late 1800s. His dream was that it would become a global second language, not replacing other tongues but acting as a unifying auxiliary. That dream never worked out for various reasons, including two rather big wars you might have heard of, but Esperanto remains a thriving global subculture with potentially a couple million speakers, including some raised with it from birth.
Esperanto is defined by its regular rules and borrowing of words from existing languages (mainly romance and germanic), which makes it famously easy to pick up, at least in comparison to the endless half-rules of natural languages. One or two aspects might take some figuring out, but almost nothing in the language has ever struck me as genuinely illogical.
Learning Esperanto in the 21st century, though, you'll probably notice pretty quickly there's something going on with gender. Even the DuoLingo course has family words as one of the first lessons. Let's demonstrate:
patro = father, patrino = mother
So the only difference between these words is that "patrino" features the -in- suffix, which denotes femininity. This is fine in theory, but the issue arises that there's no male suffix. This means that Esperanto effectively treats maleness as default, while femininity is treated as optional.
Now it's certainly true that, especially when Zamenhof created his opus, it was common for women to be treated as secondary in many regards, and languages often reflected this. But times change, and Esperanto's approach to gender is one of the only aspects that betrays its age.
And thus there have been propositions as to how one might improve the situation. The most prevalent is probably the -iĉ- suffix (eech) which is intended to be the male equivalent to -in-. So "patro" would become a neutral word for "parent", and "patriĉo" would be the new word for "father". This solution doesn't solve the problem of words like patro being sourced from the Latin word for father, but it's a definite improvement.
One quirk of the Esperanto community, though, is that there's a definite anxiety around change. This is understandable: not only does the nature of Esperanto encourage more rigidity than a traditional language, but there's been at least one significant schism in the community (the Ido offshoot) that remains controversial to this day. So a degree of trepidation makes sense.
That said, Esperanto's handling of gender has been a bit of an elephant in the room for some time, and will only feel more awkward as other languages continue to become more progressive. Something like the "iĉ" suffix is a relatively minor change, hardly a revolution that threatens any central tenet of Zamenhof's dream, and already sees a fair bit of use despite regularly causing controversy.
Esperanto was ahead of its time in many ways and remains a fascinating historical side note, and ultimately I think a language meant to unite humanity shouldn't treat half the human population as effectively second-class when simple solutions exist.