After reading Is there a policy on the use of emojis or emoticons? Here comes another question.
Sometimes I face users who have not even a single character of English in their usernames.

For example:

or

While it is the right of a person to have their username whatever they want but on the other hand sometimes it makes difficult to address those users in comment section. I know we can just copy and paste their usernames if we don't have those characters on keyboard but again that's not what I'm trying to ask. So is there any SE's policy regarding only special/Non-English characters in their username?

After reading Is there a policy on the use of emojis or emoticons? Here comes another question.
Sometimes I face users who don't have even a single character of English in their usernames.

For example:

User: 910697

User: 910677

While it is the right of a person to have their username whatever they want but on the other hand sometimes it makes difficult to address those users in comment section. I know we can just copy and paste their usernames if we don't have those characters on keyboard but again that's not what I'm trying to ask. So is there any SE's policy regarding only special/Non-English characters in their username?