util.describe_revision() trims message string to 80 characters (maybe terminal width) to display but it may breaks utf-8 byte sequence. I got UnicodeDecodeError with fixutf8 extention (which is good friend of hgsubversion for Japanese users).
The attached patch fixes it by counting column width of each character of decoded string. So the wide characters like Japanese kanji works fine.
This patch also has a change to use hgutil.termwidth() to know actual terminal width and limit to termwidth()-1 for appending LF.