This list contains some words I use even though it is not considered as standard English, or rarely used in English.
whence : from where
thou : singular second-person pronoun
: singular gender-neutral third-person pronoun
pronunciation /ziː/, similar to German sie
objective zem, possessive zer, reflexive zemself
I derived it from English determiner this, since modern pronouns also come from Old English words for this. Logically, it would more likely becomes de or fe. Fe seems out of place for me, and de may make me look like appropriating AAVE.
They as a singular pronoun kinda works, but it causes confusion. I prefer clarity, which is also the reason why I use the archaic thou when the situation allows. Of course, I respect everyone's pronoun preference so this is only used when I don't know it.