Add the appropriate HTTP header or, alternatively, add a <meta> tag. Please note that, unlike a HTTP header, the <meta> tag can be attacked more easily.
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
Furthermore, the server must be configured to send the correct charset information. In order to make these changes on the server, particular access rights are required. For further information about the different server configuration options, please refer to W3.org.
Enter in the .htaccess file:
AddType 'text/html; charset=UTF-8' html
Here is an example of an .htaccess file which will set the Header Scanner to green. (.htaccess example)