String.Format not converting integers correctly in arabic

The default behaviour for converting numeric values is "Context", which basically means if a number is proceeded by Arabic they display in Arabic (or another "non-Latin" character), if they're not then they display in "standard" European numbers.

You can change that behaviour quite easily though:

var culture = CultureInfo.CurrentCulture;
culture.NumberFormat.DigitSubstitution = DigitShapes.NativeNational; // Always use native characters
string formatted = string.Format(culture, "{0:d}{1:d}{2:d}", currentItem, of, count);

That should work as you expect - more details on MSDN.