There are at least five non-science-fictional “created languages” or IALs (International Auxiliary Language) just counting those with their own sections just in Wikipedia. (Volapuk, Esperanto, Ido, Interlingua, Interlingue (formerly Occidental). There might be others.
That list admittedly includes Volapuk (Esperanto’s immediate predecessor), which has been essentially a “dead language” for decades (most modern speakers are, as far as I know, Esperantists with a strong interest in linguistics or history). I‘m not aware that any of these other IALs ever developed an actual “culture” of its own.
There are certainly others (people keep coming up with and promoting “better” IALs) — those are just the ones that have managed to create a “Language ‘X’ section of Wikipedia.
And Toki Pona is still around, though might be unfair to “Toki Pona” to categorize it as an “International Auxiliary Language” — its purpose was significantly different. And it might credibly be considered to have its own, actual culture.
So far, Esperanto is the only IAL that’s established any genuine staying power, and it’s definitely the most commonly spoken “artificial language”. (Anyone who speaks any of the other probably also speaks Esperanto.)
