The letter Y proved inconvenient :P
There have been quite a few suggestions of names: https://wildfiregames.com/forum/topic/35736-alpha-25-name-suggestions/
Overall, we wanted to pick a name that was somewhat topical, and that excluded Yggdrasil and Yangtze.
Amharic name Yewubdar was suggested, but Amharic is posterior to our time-frame and we have not been able to confirm that it meant "beautiful beyond limits" and was not just a name.
Ynys Mons & Ysbaddaden were somewhat more topical, but lost out on votes.
This left the Persian & Maurya variant of "Ionian" most popular, and Yauna is well attested. it is also extremely topical (if perhaps a bit boring).
I have picked the spelling Yaunā with a bar on the A, though the cuneiform 𐎹𐎢𐎴 does not particularly include a final "A" glyph, unlike Xerxes.