WebClient international Url and WCF Service

Hi all.
I have a problem with SL 2b2 and WCF rest service.
title, description,... - international strings. For example: String title = "п��ове��ка";

           String searchRequest = String.Format("Title={0}&Description={1}&ISBN={2}&Category={3}&Author={4}&Language={5}", title, description, isbn, category, author, language);

           Uri searchUri  =  new Uri(HtmlPage.Document.DocumentUri, "/Service.svc/rest/booksearch?" + searchRequest);
            WebClient webClient = new WebClient();
            webClient.DownloadStringCompleted += new DownloadStringCompletedEventHandler(webClient_DownloadStringCompleted);
            webClien ...