I can't tell yet if this is a problem with ikiwiki, or rather with the web server,
or w3m, or whatever.
To reproduce:
$ LC_ALL=C w3m http://ikiwiki.info/sandbox/
Select Edit, log in, have w3m spawn an editor for editing the page and notice
that all umlauts and friends have disappeared. 
If the user now saves the page,
the mangled page will be entered into the RCS, so don't do this on the ikiwiki
sandbox page.
Yes, if you run a web browser in a non-utf8 locale, it can neither display nor properly edit unicode. --Joey