<?php

    $str = "asdas�sadsad";
    $str = preg_replace('/[^`1234567890qwertyuiop\[\]asdfghjkl;\'zxcvbnm,\.-~!@%\^&\*\(\)_\+\{\}:\|<>\?ąęćżźółńQWERTYUIOPASDFGHJKLZXCVBNMĄĘĆŻŹÓŁŃ]/i', '', $str);
    echo $str;