сойдет так ?
$dlina = mb_strlen(''.$zag['name'].'','UTF-8'); //длинна строки фамилии
$wer = '' . htmlentities($zag['name'], ENT_QUOTES, 'UTF-8') . ' ';//убираем гавно всякое
if($dlina == '3') $wer_d = '3';
if($dlina == '4') $wer_d = '4';
if($dlina == '5') $wer_d = '5';
if($dlina >= '6') $wer_d = '6';
$sovpad = mb_substr($wer,0,$wer_d,'UTF-8');