Support

The filename is converted to a random name. We do not store attachment with their original name. But that's AFTER we ask Joomla to do the pre–upload checks.

The problem is that the original filename check is part of the security check for uploading files to Joomla. This is implemented in Joomla's core code, namely Joomla\CMS\Helper\MediaHelper::canUpload, lines 224–229 in Joomla 3.10.2. If the filename contains any non–ASCII characters it is immediately rejected. 

Unfortunately, we cannot remove that check nor can we tell Joomla to NOT mind the filename — the original file name is required for the security checks which include double extension tests and content tests depending on file extension and file type. Removing this check completely would allow uploading unsafe content to your site.