sorry for this problem. How ever this add-on should read a page that is in Russian provided you have a Russian voice installed. If you are not using a Russian voice then words with Cyrillic character will not be recognize by your voice engine.
Also make sure you select the right voice for the page you want to reed or the add-on will use the default language voice of your computer. perhaps i should make the selection of voice base on the language of a page, but this has some complications i will look at it