How to check username for allowed characters?

Question

Character encoding

It used to be like this:
^[a-zA-Zа-яА-Я0-9* _-]{3,50}$
Until people from Armenia, Georgia and Greece appeared.
Well, Greek, I can add:
^[a-zA-Zа-яА-Яα-ωΑ-Ω0-9* _-]{3,50}$
But as for Chinese or Korean, it's not clear what the first character is.
Is it possible to write /ru/ in regular expressions and then you can use any Cyrillic characters?
I use UTF-8 and C# on the server, and JavaScript on the client, validation is needed both there and there.

Answer 1

Remove the tags from the input, people from these countries have always been there, I’ll say more if the last name or first name is written with a dash, there will be another trouble. Do not specify allowed, check for what should not be present.
Imagine that you write laws. It is much easier to write where you can not drink alcohol, and more effective than where you can.

Answer 2

Why would you ask like that?
en.wikipedia.org/wiki/%D0%A0%D0%B5%D0%B3%D1%83%D0%...
here
just test)