The thing is that adding that in the head section will go against the HTML tag and other metas already added by the base theme. It is better to change it in a different way. Try this steps and see if they work:
1. Edit file qa-theme/<your-theme>/qa-theme.php
2. Add or merge (if it already exists) this function:
public function initialize() {
$charset = 'iso-8859-9';
$language = 'tr';
$this->content['content_type'] = 'text/html; charset=' . $charset;
$this->content['charset'] = $charset;
$this->content['language'] = $language;
$this->content['html_tags'] = 'lang="' . $language . '"';
parent::initialize();
}
3. Check your site again