what i could do is make the A-Z bar configurable in the localisation file.This is reasonable.
But as a general comment, i have seen plenty of screenshots from asian users where the artist and tracks are still in english so the A-Z is still useful i would thinkI think English letters should be included by default in any localization file. They are usually useful.
I can foresee another problem: 26 English letters + 33 Russian letters = 59 letters. A-Z jumbar will become too wide for many screens, so either jumbar font size should be configurable or it should be possible to display jumbar in 2 rows.
but I can see no point in displaying all the letters on the A-Z jumpbar. I suggest to display only those that are preset in the Library to avoid clutter.
If there is no an artist in your music library whose name starts with R,T,Y,U for exmaple I wouldn't display these letters on the jumpbar.
Still 2 rows could be useful in some situations.
Making the A-Z jumpbar configurable in the localisation file would be useful as 'English letters' are Latin letters in general as many other alphabets, so it seems quite easy to add a few letters to customise it for any other Latin alphabet. As an example for Polish it would require to add 9 letters with diacritic marks (in the proper order).