This is BRILLIANT for anyone who has a WP site

10 Characters for Your WordPress Blacklist | Perishable Press.

We can stop that sort of garbage from scaring away visitors by adding a few lines to your Comment Moderation or Comment Blacklist (both located in your Discussion Settings). Simply add the following lines to either list:

д
и
ж
Ч
Б
Џ
Ђ
ћ
Р°
Ѓ

The beauty of this technique is its simplicity.