Though Zwiki supports InternationalCharactersInPageContent, the TextFormattingRules it relies on do not always support these characters. For example,

utf-8 in zope.conf ? Cf http://zwiki.org/FAQ#help-i-get-a-unicodedecodeerror-when-i-enter-utf-8-unicode-characters-in-restructured-text-pages

Gather details on these things here.