It seems that there is bug (or feature?) in dirify preventing from correct archiving entries with non-ASCII titles. When title of a post is non-ASCII, dirify removes all non-ASCII characters and replaces blanks with underscores. If post title consists of just one non-ASCII word, the result is empty string, and file name will look like .html.
In versions prior to 3.2 it had different behaviour, replacing non_ASCII characters with nnnn which works most of time, although name collisions were also possible.
Could somebody suggest workaround. I tried setting Basename manually on the Entry screen, but it didn't work. Meaning that new archive file was not published after rebuilding the site. Maybe another bug?