codec.cs

// hello 你好
// hello 浣犲ソ

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace EncodingTest
{
    class Program
    {
        static void Main(string[] args)
        {
            StringBuilder sb = new StringBuilder();
            string source = "hello 浣犲ソ";

            sb.AppendLine("Encoding.Default.CodePage = " + Encoding.Default.CodePage);
            sb.AppendLine("Encoding.Default.WindowsCodePage = " + Encoding.Default.WindowsCodePage);
            sb.AppendLine("Encoding.UTF8.CodePage = " + Encoding.UTF8.CodePage);

            foreach (var e1 in Encoding.GetEncodings())
            {
                foreach (var e2 in Encoding.GetEncodings())
                {
                    byte[] unknow = Encoding.GetEncoding(e1.CodePage).GetBytes(source);
                    string result = Encoding.GetEncoding(e2.CodePage).GetString(unknow);
                    sb.AppendLine(string.Format("{0} => {1} : {2}", e1.CodePage, e2.CodePage, result));
                }
            }
            File.WriteAllText("test.txt", sb.ToString());
        }
    }
}

// Encoding.Default.CodePage = 936
// Encoding.Default.WindowsCodePage = 936
// Encoding.UTF8.CodePage = 65001
//	Line 3503: 936 => 65001 : hello 你好
//	Line 17319: 50227 => 65001 : hello 你好
//	Line 17599: 51936 => 65001 : hello 你好
//	Line 18051: 54936 => 65001 : hello 你好