Constructed Languages

I will say that a huge advantage Esperanto has going for it is the number of speakers. Online, you can find many communities. Once you're in the community, you can literally couch surf the world, staying with fellow Esperantists. There's a huge corpus of reading material (I have a physical edition of The Hobbit in Esperanto), and even a few movies. It pops up here and there in popular culture, too; the name of the watch company Movado was actually taken from Esperanto.

Being popular means having chances to use the language. Not just study, and play by yourself, but interact with other people. I lurk in Ido and Lojban chat rooms, and they're mostly dead; Esperanto chat groups tend to be active.

The biggest thing, for me, is when a conlang is used for something other than just discussing the conlang itself. Esperanto has that going for it, and so it's always the conlang I return to. No, it's not perfect. Yes, it has some internal politics and debate, most lately especially around gender issues. But it has a certain momentum, and if you're looking for something you can use, Esperanto is the best choice (IMHO).

Edit 2023-07-02 I forgot to mention! There's an entire Mastodon instance dedicated to Esperanto; you're expected to post in Esperanto: https://esperanto.masto.host (fucking autocorrect made a hash of the URL; now corrected)

Obviously, a better choice would be a living language. Chinese or Hindi give you the most bang for your buck. But if you like traveling to Germany, learn German.

Heck, learning Latin is a fantastic use of time! It gives you a foot in the door to a half-dozen popular languages - enough to literally make yourself understood in a pinch.

For the internet, and if your interest is conlangs, I'd support your pick of Esperanto. Languages have the most value when there are other people to talk to with them, and Esperanto is the conlang with the most speakers, in the world, by far. Plus, it's a nice language, and will teach you a lot about languages in general. I think it's a great teaching aid for parts of speech and language construction; it's simple and straightforward.

One last caveat: Esperanto is notoriously Western influenced, and is reportedly harder for Asian native speakers. I don't believe a truly neutral language is possible, although Lojban is close: it's equally hard for everyone, regardless of native tongue. (That's a friendly dig at you Lojban folks, just a small joke).

Edit because it's a nicely done book, some eye-candy: