Well, I have a strange question. It is about my wordpress based site. It is in English and it ranked very well till I put a link to another site and the anchor text was in Cyrillic. 2 weeks later I dropped more than 10 pages in keyword ranking. My question is: Is it possible that this link in Cyrillic brakes something? Thanks.
If all you did was link to the other page then the odds are this isn't what caused your rankings to drop. One external link isn't going to cause big changes like that unless the other site is a link farm or something else that is considered against Google's Terms of Service.
The odds are that a minor algorithm change was implemented in that time or Google's index was updating and caused a temporary drop in rankings.
Either way don't do anything drastic as a result of this. You can always remove the link to the other page and see if things improve. If not then you know you need to improve the content on that page and/or seek more links to it. Internal linking is good, too, so try linking to that page from within your site more often.