MP3 tags Cyrillic chars

I don't have any Cyrillic characters in my music collection but I can do Greek with no problem using the latest version of eyed3 installed by sudo pip install --upgrade eyed3:

 $ eyeD3 Μπεστ\ οφ/Τζίμης\ Πανούσης\ -\ Κάγκελα\ Παντού.mp3 
Τζίμης Πανούσης - Κάγκελα Παντού.mp3    [ 3.43 MB ]
-------------------------------------------------------------------------------
Time: 03:45 MPEG1, Layer III    [ 128 kb/s @ 44100 Hz - Joint stereo ]
-------------------------------------------------------------------------------
ID3 v2.4:
title: Tzimis Panousis-Kagkela Pantou.mp3
artist: Tzimis Panousis
album: Unknown

In the example above, I have a directory (album name) called Μπεστ οφ which contains a song called Κάγκελα Παντού by Τζίμης Πανούσης. As you can see in the id3tool output above, the tags are not in Greek. Let's fix that:

$ eyeD3 -A "Μπεστ οφ" \
        -t "Κάγκελα Παντού" \
        -a "Τζίμης Πανούσης" \
        "./Μπεστ οφ/Τζίμης Πανούσης - Κάγκελα Παντού.mp3"

That correctly set the tags using the Greek alphabet:

$ eyeD3 Μπεστ\ οφ/Τζίμης\ Πανούσης\ -\ Κάγκελα\ Παντού.mp3 
Τζίμης Πανούσης - Κάγκελα Παντού.mp3    [ 3.43 MB ]
-------------------------------------------------------------------------------
Time: 03:45 MPEG1, Layer III    [ 128 kb/s @ 44100 Hz - Joint stereo ]
-------------------------------------------------------------------------------
ID3 v2.4:
title: Κάγκελα Παντού
artist: Τζίμης Πανούσης
album: Μπεστ οφ

OK, but since the information is encoded in the name of the file, this can be automated. In the example above, the file name has this format:

Album/Artist - Title.mp3

So, we can parse and add the tags for all files with a little shell magic:

find . -type f -name "*mp3" | while read file; do 
    album="$(basename "$(dirname "$file")")"; 
    filename="$(basename "$file")"; 
    artist=${filename%%-*}; 
    title=${filename##*-}; 
    title=${title%%.mp3}; 
    eyeD3 -A "$album" -t "$title" -a "$artist" "$file"; 
done

After running this command, all files will have had their id3 tags modified:

  

I could succesfully update an MP3 file using:

eyeD3 -a "Ю" abc.mp3

This was done with eyeD3 0.7.4-beta as installed using pip from PyPI:

pip install eyeD3

Using that eyeD3 you could use a script to extract the artist and title from the MP3's file path and set them as ID3v2 2.4 tags with eyeD3.

Alternatively, you can use the mid3iconv utility from the python-mutagen package:

$ mid3iconv
Usage: mid3iconv [OPTION] [FILE]...

Mutagen-based replacement the id3iconv utility, which converts ID3 tags from
legacy encodings to Unicode and stores them using the ID3v2 format.

Options:
...
  -e ENCODING, --encoding=ENCODING
...
  --force-v1            Use an ID3v1 tag even if an ID3v2 tag is present
  --remove-v1           Remove v1 tag after processing the files

So, basically, running

mid3iconv -eCP1251 --remove-v1

will yield exactly the result you're looking for.