using System;

using System.Globalization;

public class Program

{

    public static void Main()

    {

        var date = new DateTime(1900, 12, 11);

        var enUs = new CultureInfo("en-US");

        var enGb = new CultureInfo("en-GB");

        var deDe = new CultureInfo("de-DE");

        var strUs = date.ToString(enUs);

        var strGb = date.ToString(enGb);

        var strDe = date.ToString(deDe);

        Console.WriteLine(strUs);

        Console.WriteLine(strGb);

        Console.WriteLine(strDe);

        Console.WriteLine("-------------------------");

​

        var inputEnUs = "Apr 6, 2009";

        var inputEnGb = "06-Apr-2009";

        var inputFrFr = "6 avr. 2009";

        var inputDeDe = "06.04.2009";

        var inputs = new [] {inputEnUs , inputEnGb, inputFrFr, inputDeDe };

        foreach (var dateString in inputs) {

            var output = ParseMultiCulture(dateString);

            Console.WriteLine(output.ToString("yyyy-MM-dd"));

        }

    }

    private static DateTime ParseMultiCulture(string dateString) {

        DateTime output;

        string[] formatsEnUs = {"MMM d, yyyy"};

        string[] formatsEnGB = {"dd-MMM-yyyy"};

        string[] formatsFrFr = {"d MMM yyyy"};

        string[] formatsDeDe = {"dd.MM.yyyy"};

        if (DateTime.TryParseExact(dateString, formatsEnUs, new CultureInfo("en-US"), DateTimeStyles.None, out output)) {

            return output;

        }

        if (DateTime.TryParseExact(dateString, formatsEnGB, new CultureInfo("en-GB"), DateTimeStyles.None, out output)) {

            return output;

        }

        if (DateTime.TryParseExact(dateString, formatsFrFr, new CultureInfo("fr-FR"), DateTimeStyles.None, out output)) {

            return output;

        }

        if (DateTime.TryParseExact(dateString, formatsDeDe, new CultureInfo("de-De"), DateTimeStyles.None, out output)) {

            return output;

        }

        throw new NotSupportedException("Given datestring is in a format that is not supported.");

   }

}