using System;
using System.Globalization;

class Test
{
    static void Main()
    {
       CultureInfo ci = CultureInfo.GetCultureInfo("de-DE"); // German       
       double d = 123.23;
       string s = d.ToString(ci);
       Console.WriteLine(s); // 123,23

       CultureInfo ci2 = CultureInfo.GetCultureInfo("en-US"); // US English
       double d2 = double.Parse(s, ci);
       string s2 = d2.ToString(ci2);
       Console.WriteLine(s2); // 123.23

       Console.ReadKey();        
    }
}