using System;

using System.Globalization;

public class Program

{

    public static void Main()

    {

        // decimal.ToString: https://msdn.microsoft.com/en-us/library/fzeeb5cd(v=vs.110).aspx

        Console.WriteLine("Ordinary ToString, depending on installed environment              : {0}", 123456.789123.ToString());

        Console.WriteLine("en-US culture. Might be what you are looking for, but probably not : {0}", 123456.789123.ToString(new CultureInfo("en-US")));

        Console.WriteLine("sv-SE culture. Switching comma and period                          : {0}", 123456.789123.ToString(new CultureInfo("sv-SE")));

        // Probably the correct one. See: https://msdn.microsoft.com/en-us/library/system.globalization.cultureinfo.invariantculture(v=vs.110).aspx

        Console.WriteLine("Invariant culture. Basically \"English\"                             : {0}", 123456.789123.ToString(CultureInfo.InvariantCulture)); 

        Console.WriteLine();

        Console.WriteLine("For dates though Invariant is a bad choice");

        Console.WriteLine("as it leads to Yoda format : {0}", DateTime.Now.ToString(CultureInfo.InvariantCulture));

    }

}