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.
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