PSML documents whose names contain diacritic characters are not displayed. If a users creates such a document (e.g. page) with J2 administrative mechanisms or manually as a file it appears in a portal but is not rendered. I cannot see any error logs about it as if the resource was not found at all. I guest it has something to do with URL encoding.
I've noticed the problem on windows, where cp1250 encoding was used. It might not appear if the OS and Jetspeed encodings are the same.