First, change the output encoding to UTF8:
Console.OutputEncoding = Encoding.UTF8;
Console.WriteLine("добры дзень");
Now you’ll still see question marks. The reason is that the default console’s font doesn’t support Cyrillic letters. Change the font of the console:
If you’re lucky, you should find a different font with Unicode support:
Change the font, and you should be able to see your text:
In the general case, if you want to display all Unicode characters reliably, the Console is probably not right for you. See also: C# console font (the comments are interesting too)