An explanation of this issue can be found at: https://github.com/mpatric/mp3agic/issues/39
In summary, the problem is that the text encoding is windows-1251 (also known as cp1251). ID3v2 tags with windows-1251 encoded strings (or any other encoding that's not one of the 4 supported encodings for ID3v2) are not valid. Programatically differentiating windows-1251 from iso-8859-1 is not easy, so automatically detecting the strings in order to transcode them might be tricky.
Some interesting comments here: https://superuser.com/questions/495775/how-to-translate-wacky-metadata-to-readable-format