@[email protected] -- Just looked again... this was first introduced as a hidden feature in redmatrix around 2013-2014, and so may also be available currently in Hubzilla (behind the "system.unicode_usernames" feature toggle). There were some major changes in 2019 that to my knowledge weren't ever backported. I think these only applied to local usernames and not remote usernames, but the functionality in hubzilla still might need to be verified.