I have a problem with Turkish characters in my programme. I take a string from webbrowser's source like this

string mySource = webBrowser1.DocumentText;

The site where I get the source from, contains Turkish characters in InternetExplorer source. But when I get that source from C# with the code above and show it in MessageBox or Textbox, it shows "?" instead of Turkish characters and when I convert the string to char those characters are shown as spaces.

What should I do to solve the problem?