charset of a page loading in a iframe not shows correctly

I am using XE 2.0.3 and 2.1. I try to use construction <iframe src=...>. I want to show doc.html (text on russian, or romanian). Unfortunatly, the visual look of iframe on a xwiki page are wrong - incorrect charset. For XWiki Internationalization Setup I made all as of described at "Administrators Guide". Jetty, database, xwiki - all is utf-8. Also and my doc.html is utf-8. I checked this in a sourcecode of my doc.html and sourcecode of a wiki-page. All is same and utf-8. Also, if I try to load my doc.html as a separate web-page - all is ok - and utf-8. Problem exists only if I use <iframe src=...> in xwiki. As I understand, it is a known problem. For example, same situation I found here: http://www.opennet.ru/openforum/vsluhforumID8/3063.html (unfortunately on russian). Also some web-application on java, also iframe, also same charset of a main page and iframe-page ... They said, that problem created from the javascript function iframe.DesignMode = "On" and they resolved issue. Maybe it is possible to solve this situation also in xwiki? It will be great!