The Filename of the attached report file for a report over a period (weekly, monthly, etc) contains a invalid character (en dash / u+2013), which causes some mail clients aren't able to open the mail / attachment.

The filename must built following the rules of the RFC 5987 to allow characters which aren't in ASCII or ISO-8859-1.

Be aware that the filename is identical to the subject of the mail plus the file extension. I did a quick fix changing all en dashes in ./plugins/Intl/lang/de.json (for my use only in german) into dash inside of ASCII code table.