using System;

using System.Globalization;

using System.Threading;

public class Program

{

    public static void Main()

    {

        var double1 = 1.23;

        var bytes1 = BitConverter.GetBytes(double1);

        Console.WriteLine(double1);

        CultureInfo customCulture = (CultureInfo)Thread.CurrentThread.CurrentCulture.Clone();

        customCulture.NumberFormat.NumberDecimalSeparator = ",";

        Console.WriteLine(string.Format(customCulture, "{0}", BitConverter.ToDouble(bytes1, 0)));

​

    }

}