PHP preg_match不允许æøå

I am trying to make my registration script accept only letters and æøå, but nothing I've tried so far has worked. It still won't accept æøå.

This is my code so far

if ($_POST['first'] != "" && preg_match("%^[-a-zA-Z æøå\/]+$%", $_POST['first']) == true && strlen($_POST['first']) > 0) { 
    $input_first = mysqli_real_escape_string($con,$_POST['first']); } 
else { header("Location: ../register.php?n=2"); exit; die(); }

What am I doing wrong?

If your PHP file is already UTF-8 encoded, you should tell your database, that you need UTF-8. Instead of fiddling with the configurations of MySQL, just tell your connection object, which character-set you expect, the database does the rest for you.

This is an example for a mysqli connection object:

 //Test-ak
  $db = new mysqli($dbHost, $dbUser, $dbPw, $dbName);
  $db->set_charset("utf8");

Afterwards your queries will return UTF-8 encoded results.