You run the Export-PublicFolderStatistics.ps1 script in an Exchange Server 2016 environment. If there are Russian (Cyrillic) characters in public folders, those characters are displayed as question marks (?) in the export results.
To fix this issue, install Cumulative Update 1 for Exchange Server 2016 or a later cumulative update for Exchange Server 2016.
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.
Learn about the terminology that Microsoft uses to describe software updates.