$result = Db::getInstance(_PS_USE_SQL_SLAVE_)->executeS('
            SELECT cl.*,c.*, cl.`name` AS country, zz.`name` AS zone
            FROM `'._DB_PREFIX_.'country` c'.
            Shop::addSqlAssociation('country', 'c').'
            INNER JOIN `'._DB_PREFIX_.'country_lang` cl 
                ON(c.`id_country` = cl.`id_country` 
                AND cl.`id_lang` = '.(int)$id_lang.')
            INNER JOIN `'._DB_PREFIX_.'carrier_zone` cz 
                ON(cz.id_zone = c.id_zone)
            INNER JOIN `'._DB_PREFIX_.'carrier` cr 
                ON(cr.id_carrier = cz.id_carrier 
                AND cr.deleted = 0 '.
                ($active_carriers ? '
                    AND cr.active = 1) ' : ') ').'
            LEFT JOIN `'._DB_PREFIX_.'zone` zz 
                ON(cz.id_zone = zz.id_zone 
                AND zz.`id_zone` = c.`id_zone`)
            WHERE 1
            '.($active_countries ? '
                AND c.active = 1' : '').'
            '.(!is_null($contain_states) ? '
                AND c.`contains_states` = '.(int)$contain_states : '').'
            GROUP BY c.`id_country`
            ORDER BY cl.`name` ASC
        ');

Et non, le distinct n'est plus utile.