add_filter( 'gettext', 'change_pending_in_pmpro', 20, 3 );
function change_pending_in_pmpro( $translated_text, $text, $domain ) {

        switch ( $translated_text ) {

            case 'Pending' :

                $translated_text = __( 'CHANGE THIS TEXT', 'paid-memberships-pro' );
                break;

        }

    return $translated_text;
}