i have replaced
utf8mb4 with utf8
and
utf8mb4_unicode_ci with utf8_general_ci
then all the data perfectly imported.
`meta_id` bigint(20) unsigned NOT NULL AUTO_INCREMENT,
`comment_id` bigint(20) unsigned NOT NULL DEFAULT '0',
`meta_key` varchar(255) CHARACTER SET utf8 COLLATE utf8_general_ci DEFAULT NULL,
`meta_value` longtext CHARACTER SET utf8 COLLATE utf8_general_ci,
PRIMARY KEY (`meta_id`),
KEY `comment_id` (`comment_id`),
KEY `meta_key` (`meta_key`(191))
) ENGINE=MyISAM AUTO_INCREMENT=3789 DEFAULT CHARSET=utf8;