there's a word in toki pona, "yupekosi", that word means "to do like George Lucas and revise a previous creative work and make it worse". the joke is that the inclusion of the letter "y" does that to the language itself. no one knows how to pronounce it because the language does not otherwise use that letter (and "j" already makes the sound you'd expect "y" to). so that means toki pona has undefined behavior.