<?
if ($is_logged == TRUE){

$pm_un_num_mvl = substr($member_id['pm_unread'], -1);
if (substr($member_id['pm_unread'], -2, 1) != 1 or $member_id['pm_unread'] < 10 ) {
    switch ($pm_un_num_mvl):
    case 1:
    $pm_un_num_mvl = $member_id['pm_unread'] . ' новое сообщение';
    break;

    case 2: case 3: case 4:
    $pm_un_num_mvl = $member_id['pm_unread'] . ' новых сообщения';
    break;

    case 5: case 6: case 7: case 8: case 9: case 0:
    $pm_un_num_mvl = $member_id['pm_unread'] . ' новых сообщений';
    break;
    endswitch;
} else {
    $pm_un_num_mvl = $member_id['pm_unread'] . ' новых сообщений';
}

у Вас <a href="{$link_pm}">{$pm_num_mvl}</a>