i can't confirm if it's a bug because i have japanese support already installed in win98 so can't reproduce without uninstalling it first.
for now , you need to download this:
http://www.microsoft.com/windows/ie/ie6/downloads/recommended/ime/install.mspx
select japanese with language pack or additional languages if you'll need them.. this should install the required fonts wikipedia is asking for. once the fonts are installed to the fonts folder, k-meleon should see them and call them when a site requires a specific language font.