using System;

using System.Globalization;

using System.Linq;

public class Program

{

    public static void Main()

    {

      string startdate = @"٢٠١٩-٠٩-٠٣";

​

      string translated = string.Concat(startdate.Select(c => char.GetNumericValue(c) < 0 

        ? c.ToString()                          // Character, keep intact  

        : char.GetNumericValue(c).ToString())); // Digit! we want them be 0..9 only

​

      // Arabic language has right to left order, that's why pattern is "yyyy-M-d"

      DateTime dateTime = DateTime.ParseExact(

        translated, // note, not startdate

       "yyyy-M-d", 

        CultureInfo.InvariantCulture, 

        DateTimeStyles.AssumeLocal);

​

      // English, Great Britain culture

      Console.Write(dateTime.ToString("d MMMM yyyy", CultureInfo.GetCultureInfo("en-GB")));

    }

}