The name...
- has to be recognisable as a first name.
- can't be a surname.
- has to be unambiguously male or female.
- can't compromise the well-being of the child.
- can't have a relation to something "evil" (for example
Judas).
- can't be offensive to religion.
- can't be a place name.
- can't be a title.
Like I said, it could very well be that
Steffi would be permitted, though legit names like for example
Beauregard have been rejected before. It would be up to the person who gets to record the name whether
Steffi would be legit or not.