How can i convert English digits to Arabic digits?

Thy this workaround (just list all cultures you want to use this numerals in the string array):

private static class ArabicNumeralHelper
{
    public static string ConvertNumerals(this string input)
    {
        if (new string[] { "ar-lb", "ar-SA" }
              .Contains(Thread.CurrentThread.CurrentCulture.Name))
        {
            return input.Replace('0', '\u06f0')
                    .Replace('1', '\u06f1')
                    .Replace('2', '\u06f2')
                    .Replace('3', '\u06f3')
                    .Replace('4', '\u06f4')
                    .Replace('5', '\u06f5')
                    .Replace('6', '\u06f6')
                    .Replace('7', '\u06f7')
                    .Replace('8', '\u06f8')
                    .Replace('9', '\u06f9');
        }
        else return input;
    }
}

Then use the method, for all of your strings you want to have 'central Arabic numerals' in, like this:

DateTime.Now.ToString().ConvertNumerals();

As a quick test, I wrote this to list all the cutures which don't have "2010" in the year:

        foreach (var ci in 
            from c in CultureInfo.GetCultures(CultureTypes.AllCultures)
            where !c.IsNeutralCulture
            let date = DateTime.Now.ToString("MMMM dd, yyyy", c)
            where !date.Contains("2010")
            orderby c.Name
            select new {c.Name, date})
        {
            Console.WriteLine("{0} : {1}", ci.Name, ci.date);
        }

the results are:

ar-SA : ربيع الأول 05, 1431
dv-MV : ربيع الأول 06, 1431
prs-AF : ربيع الأول 06, 1431
ps-AF : ربيع الأول 06, 1431
th-TH : กุมภาพันธ์ 19, 2553

To convert the numbers to Arabic text, it looks like this "NumToArabicString" project will do it. It doesn't look like there's anything built into the .net framework though.