How to solve htmlspecialchars and encoding problem?

Question

PHP

Warning: htmlspecialchars(): charset `utf8' not supported, assuming utf-8 in ....domain/core/model/modx/modx.class.php on line 292

foreach ($targets as $target) {
            $_SERVER[$target] = isset ($_SERVER[$target]) ? htmlspecialchars($_SERVER[$target], ENT_QUOTES) : null;
        }

And another line

Warning: htmlspecialchars(): charset `utf8' not supported, assuming utf-8 in ....domain/core/config/config.inc.php on line 292

$http_host= array_key_exists('HTTP_HOST', $_SERVER) ? htmlspecialchars($_SERVER['HTTP_HOST'], ENT_QUOTES) : 'mydomain.ru';

What's the trouble, modx does not allow you to install any plugin.