- elvish: fan versions of finnish and gaelic
- klingon: generically "foreign" language that cribbed most of its consonant inventory from indigenous languages of the pacific northwest
- dothraki: not gonna make a joke about this one cuz i know the guy who made it lol
- toki pona: accidental auxlang that makes it equally hard for everyone to express things!
- esperanto: a polish jew put romance languages in a blender to prevent wwii from happening again
- ido: esperanto 2.0 that got forked because of drama
- ithkuil: a conlang with the cool feature that no one on the entire world can pronounce it
- loglan: conlang with no ambiguity whatsoever, so computers can definitely parse it. too bad no one speaks it
- lojban: the ido of loglan
- “elvish”: tolkien actually famously disliked gaelic, and neither quenya nor sindarin are based on it. quenya draws inspiration largely from finnish and latin, and sindarin from welsh, but neither is actually a straightforward imitation of their inspirations whatsoever
- klingon: i hope this doesn't come off as too unkind, but are you really familiar with the phonologies of any indigenous languages of the pacific northwest? in common with them klingon has a lateral affricate and some uvulars, which are found in languages across the world, while it entirely lacks their characteristic glottalized consonants and very permissive syllable structure. klingon is not “generically ‘foreign’”, it's unnaturalistic by design, with a phonaesthetic not strongly comparable to any single human language or language family.
- dothraki: however you feel about it, it's a language far better than george rr martin's lazy-ass fremen mirage-ass worldbuilding deserves
- toki pona: yeah i mean i'm not sure how making precision of communication difficult makes a language an auxlang at all but sure
- esperanto: zamenhof was born in białystok and raised his children as polish-speakers but he himself grew up bilingual in russian and yiddish. he also died in 1917, in the middle of the first world war, while esperanto was first published way back in 1887. so i dunno about this one
- ido: has certainly caused a lot of drama since its split from esperanto, but originated not as an arbitrary fork but from a movement within the esperanto community based on zamenhof's own 1894 “reformed esperanto”
- ithkuil: i think i'm going to have to call this one a skill issue. ithkuil in its modern form has a pretty modest 31 consonants and 9 vowels, and though it does allow a lot of consonant clusters, a significant amount of thought has been put into making sure that there's nothing actually unpronounceable
- loglan: nobody speaks it because lojban exists,
- lojban: which actually did fork from loglan over (copyright) drama, but which unlike ido managed to capture almost the entire speaker base, which is significant in size and highly active