Hi!
Cyrillic letters would need the database to be in UTF-8 which is only available for new installs of FreePBX 13.
see:
That said I was able to convert my database to UTF-8 by doing this:
but this is unsupported and might not work as well for you as it did for me...
If you want to try this make a backup first...
If you had somehow managed to type in Cyrillic letters before the upgrade (if your database was in ISO-8859-1 like mine I doubt you did since it doesn't support Cyrillic) they will have been corrupted and you will need to retype those entries...
I tested my database using both Cyrillic, French and Romanian letters and everything seemed A-OK... I cannot say I tested all of the screens with all of those alphabets but I made sure my database post-conversion supported characters which were already supported by ISO-8859-1 (like French) or needed either their own character set or UTF-8 (like Cyrillic and Romanian).
The problem with the apostrophe I mentioned (and other similar issues) where later fixed by module updates.
I had a (different) problem which later required me to restore my database but I restored from a backup of that converted database and everything is still working perfectly.
I just tried again after reading your message to type in a few Cyrillic letters and it definitely seems to work perfectly...
Good luck and have a nice day!
Nick