@solmedia. Thanks for posting, and thanks for being a solid customer for so many years. I appreciate the support.
With Easy Folder Listing Pro, the filenames are not stored in a database, they are taken directly from the file system. As such, the key to get the files to display correctly is actually the charset encoding that is set when you upload the files to your server using your FTP client. If the charset encoding of the file system or the encoding used by the FTP client is not UTF-8 then you will get artifacts like that.
I would try to re-upload the files with the charset encoding of my FTP client specifically set to UTF-8. Try that and see if it works. I do have features to tweak the charset encoding in the “Options” for the component that you could try. You can access it from the “Options” button on the top right hand side of the Dashboard or Profile Manager.