How to request KOI8-R documents when several encodings available

There is the method to instruct the server to give you a document in requested character set passing it via HTTP_ACCEPT_CHARSET variable.

Check variables your browser passes to HTTPD using this CGI Test Script

If your browser ask for file downloading instead of page displaying, it can't handle
Content-Type: type; charset=name
in HTTP header, bug its development team.

If your browser is able to request character set (Russian KOI8-R character set assumed in example below), you'll have KOI8-R in HTTP_ACCEPT_CHARSET field. For example:

HTTP_ACCEPT_CHARSET = KOI8-R, ISO-8859-1; q=0.1