Netscape Messenger can not handle belarusian texts properly. The same applies to Mozilla.
Mutt handles a multitude of charsets and encodings with ease. If your console has windows-1251 support, add the following lines to your .muttrc:
charset-hook "windows-1251" "cp1251" set charset="windows-1251" |
Mutt automatically converts all incoming messages for the screen output. It can also convert outgoing messages basing itself on a versatile pattern matching mechanism, e.g. the following line in .muttrc will force mutt to convert all messages sent to be-locale@iatp.unibel.by to koi8-r.
send-hook '~t ^be-locale@iatp\.unibel\.by$' 'set send_charset="koi8-r"' |