Cyrilic letters problem

I`m trying to translate the forum on Bulgarian. But when i write whatever cyrilic letter in /lang/index.php the whole text in the ' ' disappear. Like this  'Moderated by'                =>  'Сашо Moderated by %s' .... or this 'Moderated by'                =>  'С Moderated by %s',. Can anybody help me to find and avoid the function, that cuts it. I found forum_remove_bad_characters();, and commented it, but the result is the same.