The Channel Properties Window ("Channel Central") does not support UTF8 channel topics (probably also not UTF8 nicknames in banlist). You'll get a raw encoded channel topic displayed. Also it's not possible to use UTF8 characters for topic change in this box.
48.Added support for display of UTF-8 text as unicode in status, channel, query, and other windows, and in nickname listboxes, window titlebars, switchbar, and tooltips.
mIRC makes no mention of supporting channel central.