using System;

using System.Globalization;

public class Program

{

    public static void Main()

    {

       string str = "09/12/2018";

       DateTime dt = DateTime.ParseExact(str, "dd/MM/yyyy", null);

       Console.WriteLine("US: " + dt.ToString(new CultureInfo("en-US"))); //1/31/2018 10:00:00 AM       

       Console.WriteLine("AU: " + dt.ToString(new CultureInfo("en-AU"))); //1/31/2018 10:00:00 AM       

       Console.WriteLine("UK: " + dt.ToString(new CultureInfo("en-GB"))); //31/01/2018 10:00:00

    }

}