/**
 * prepares a string optimized for SEO
 * @param string $sString 
 * @return string $sString SEO optimized string
 */
function seofy ($sString = '')
{
    $sString = preg_replace ('/[^\pL\d_]+/u', '-', $sString);
    $sString = trim ($sString, "-");
    $sString = iconv ('utf-8', "us-ascii//TRANSLIT", $sString);
    $sString = strtolower ($sString);
    $sString = preg_replace ('/[^-a-z0-9_]+/', '', $sString);

    return $sString;
}

_____

echo seofy('Straßenfest in München');          // => strassenfest-in-muenchen
echo seofy('José Ignacio López de Arriortúa'); // => jose-ignacio-lopez-de-arriortua