RegEx for Username validation

Question

im a very beginner in RegEx.

I search a RegEx that validates if a string (username) is at least 3 chars, has no number or special char (ü, ö, ä) in firstspace, and no other special char else then üöä in total string.

Any help please?

Answer 1

^[a-zA-Z][a-zA-Z0-9üöä]{2,}$