using System;

using System.Text;

using System.Web;

public class Program

{

    public static void Main()

    {

        var myString = "æøå_äöü";

        Console.WriteLine(Normalize(myString));

    }

    static string Normalize(string source)

    {

        string textEncode = HttpUtility.UrlEncode(source, Encoding.GetEncoding("iso-8859-7"));

​

        string textDecode = HttpUtility.UrlDecode(textEncode);

​

        return textDecode;

    }

}