Okay, so I was just screwing around, and then I found a file called 'AUIbackup' and it housed some information. One thing I got was something about a Zora Interface in some location. I went to said file location, and opened up one or two of the images, they winded up being images for HYRULE! This could possibly explain the dumb-screwyness of the interfaces, almost all the UI interfaces for "Civilized" are just copy-paste of hyrule. This could lead to a fix, or I could have just stumbled upon a faux location. Whichever it is, I dunno, but I'm currently resaving all the stuff under "AUI>Zora> to data>ui/northern_european/interface to see if it'll work once I boot my game, if it does, I'll post back here saying what all the conversions are. Until then, peace.
EDIT: Worked, once I edited I pressed 1 then 2 on the UI selection screen, which gave me a Zora UI for hyrule, and I'm currently trying to see if I'll get a Zora UI for hyrule if I do 1>1 on the UI interface. I'll post back again once I check that.
EDIT: It worked. Here's all the conversions to help you guys! BTW, before you begin editing, go into ui>[vanilla conversion for your faction]>interface and right-click. At the bottom of the right click menu will be something called "properties", go there and go to "security" from there go down to "edit" **IMPORTANT** I'm pretty sure you have to be logged in as the Administrator on your computer to edit this. in the "edit" menu, click the one at the bottom, should say something about "users" and go down and check the box for "Modify", this will allow you to cross-save the UIs. Now, here's the list!
All Civilized factions fall under "northern_european", I'm not entirely sure how, but I managed to get both Zora and Hylian even though I edited in there, so you should be fine (i think? I don't really know what I'm doing, so some of this is going to be hit and miss)
Barbaric factions are under "barbari_european"
Naturalistic are under "southern_european"
Unnatural are under "greek"
and I'm pretty sure that's it. I didn't include Gohma or Twili because those have their own cultural thing. Hope this helps!
EDIT: Turns out you only need to convert once and they'll all work for that cultural group, simply replace ONE faction UI in the vanilla coding section and every UI in the culture will be available to you.