[exim] Local EAI addresses ?

I'm trying to set up an exim server with UTF-8 aka EAI local addresses.

I'm using the FreeBSD 4.94 package which has all of the EAI options turned
on, and I can send mail to EAI addresses other places so I think my
overall config is mostly right.

What I would like to do is to have some local UTF-8 addresses that deliver
to local maildirs so I have this fairly ugly router:

my_switch:
driver = accept
local_parts = ${lookup{$local_part}lsearch{/etc/mail/myfake}}
transport = my_mailboxes

and this transport

my_mailboxes:
driver = appendfile
directory = /var/maildir/${local_part_data}/
user = johnl
maildir_format
delivery_date_add
envelope_to_add
return_path_add
group = mail

The file /etc/mail/myfake contains:

user1: user1
用户1: user1

(If the second line is smashed, the it's two chinese characters followed by digit 1)

Sending mail to user1 works fine. Sending mail to 用户1 bounces with unknown user:

2020-07-31 19:26:19 1k1ePr-0000iX-8I <= johnl@??? U=johnl P=local S=431
2020-07-31 19:26:19 1k1ePr-0000iX-8I ** 用户1@???: Unknown user

Any suggestions? Are UTF-8 local mailboxes supposed to work?

R's,
John