You already answered most of the questions I had, but do you remember how it managed multiple character sets? I'm especially curious about how it supported Japanese Kanji, given how many characters that has. Some quick searching suggests maybe it was XCCS[1]? I had no idea that Xerox was so far ahead of their time that they invented a sort of proto-Unicode when many computers didn't even support lowercase letters.
[1] https://en.wikipedia.org/wiki/Xerox_Character_Code_Standard
Edit: fixed typo
I was at one time on the XCCS committee and involved with Unicode development before it was called Unicode when I was at Both Xerox and Apple.
A lot of the Japanese feathers were developed with Fuji Xerox, namely vertical text support but the typing method virtually keyboard support was done by the international team headed by Joe Becker who was the Architect of all the multilingual stuff.
Albert in his comment preceded my involvement some trust what he says about earlier development over what I remember.
I didn't deal directly with the Kanji, but Fuji Xerox sent quite a few of their engineers over to help. They played on our softball team.
Also, https://www.digibarn.com/collections/screenshots/xerox-star-... shows the date as "Tuesday May 15", which occurred in 1984 but not 1981.
Further down it has a window with "9-Feb-84", consistent with this being from 1984.
And https://www.digibarn.com/collections/screenshots/xerox-star-... has date from 1983.