Non ASCII characters in file names

Dear all,

my students uploaded  their assignements with file names containing non-ASCII characters, and upon dowloading and attempt to unzipp on my Ubuntu-Linux I realized ???-chars instead of some characters, like (see the attachement):

...Kráľová... -> ....Kr??????ov???...

(Unzipping of such a file is not working on Ubuntu, I should try it on Windows).

We are using moodle 2.5.

Any help, please ?

Miro Ilias