Currently there is no way to force MC to use UTF8 with ftp servers.
When connecting to a FTP server, MC will ask the ftp server about what features it support and if it say it support UTF8 then UTF8 will be used for getting file list and such.
If you look in the ftp connection log, at the beginning is there a "> FEAT" line ? and the following list after that is a list of features the FTP server support.