We have checked this and don't see such an issue. Please make sure the PO/.MO file is located in the wp-content\languages\plugins folder and the filename is correct. 

Hi, and thanks for the tip, but the file wpdiscuz-it_IT.po with its wpdiscuz-it_IT.mo, both located in the wp-content\languages\plugins and wp-content\plugins\wpdiscuz\languages folders. The po/mo files they were created from your wpdiscuz.pot file, located in the folder wp-content\plugins\wpdiscuz\languages so it's a bug. If you look for the related php file string you will find the error!