We have dovecot IMAP server with users' mailfolders. Some users use Cyrillic folder names. The folders' names readable in Thunderbird, but non readable on the server. See RFC 2060.
There is some partial solution. To read Russian folder names start the following command in the mailfolder (or set necessary path to mailfolder instead of dot in the find command):
find . -maxdepth 1 -type d|cut -c4-| sed 's/\&/+/g'|iconv -f utf-7