The problem was that in HTML pages, the content of the link (between double square brackets) was not unescaped. I would not recommend to use funny characters, but since one can upload these files, this was clearly a bug in xowiki's link handling (now fixed in CVS).
All the best
-gustaf
http://cvs.openacs.org/changelog/OpenACS?cs=MAIN%3Agustafn%3A20111108123042
