I'm not sure that your incoming strings will be UTF-8, or rather, the incoming strings might contain UTF-8 but they might not be tagged with the utf8 flag in Perl. It's much of guesswork what encoding browsers use on form submissions - a rule of thumb is that the browser might use the same encoding the page was sent with... So inspect the bytes you get back and maybe manually switch the UTF-8 flag on on your $nachname variable - then the (utf8) regex should/could/might actually match. You could also enlist the help of demerphq :)

If that approach of tagging (or encoding) the data fails, maybe turn the regex around and reject what is not allowed:

my @rules = (
    # presuming ASCII machine
    # this will likely break on an EBCDIC machine
    [ qr/\x00-\x1f/,'Keine Steuerzeichen erlaubt' ],
    [ qr/\d/,'Keine Zahlen erlaubt' ],
    [ qr/!-@/,'Keine Sonderzeichen erlaubt' ],
    [ qr/\[-`~/,'Keine Sonderzeichen erlaubt' ],
    # ...
);

for (@rules) {
    my ($rule,$message) = @$_;
    if ($nachname =~ /$rule/) {
        die $message;
    };
};
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