@thescrapyard
I guess the issue is related to the fact that SubtitlesCreator, the app used to convert from SRT to SUP, accepts only ANSI formatted text. If the input SRT file is formatted in UTF format (and your file should be like that), than A2D converts the content to ANSI. During conversion many special chars are lost, very likely cyrillic chars are lost as well.
BTW to be sure of that guess, let's wait for the russian subs file.
Bye