Regarding Media Library displaying unreadable characters for foreign language diactritical marks or glyphs such as Éé, Èè, Êê, Ëë (French):
I originally ripped my CD collection with Exact Audio Copy, so long ago. The file names on my PC contained the glyphs, such as "Gymnopédie No.1 - Lent et douloureux.wav", but the library displayed # for é. After some research I realized that Exact Audio Copy must have had the unicode support to write the file name correctly, but not in the ID3 Tags.
The fix was to copy to the correct file / album name from the internet and paste it into the tag in JRiver, and then update the IDV3 tag in the actual file on the PC by highlighting/selecting the songs/albums in the library, and then going to Tools>Library Tools>Update Tags From Library.
This procedure fixed the ID3 tag in the actual file on my PC and forever made the problem go away!
To check it you can Update Library From Tag and see, that when the ID3 tag is imported from the file its still correct. Hope this helps someone.