Adding a non-english username using useradd

Hi,

I am not able to add a user in japanese language using the useradd command

[root@ssnr28a_01 ~]# useradd 誰か
useradd: invalid user name '誰か'

I am using Red Hat Enterprise Linux Server release 7.4 (Maipo)
I copied the username using google translator.
I also tried setting LANG

[root@ssnr28a_01 ~]# echo $LANG
ja_JP.UTF-8
[root@ssnr28a_01 ~]# useradd 誰か
useradd: '誰か' はユーザ名に使えません
which translates to "invalid user name"

Is username and groupname in non-english not supported?

Thank you