There is no support in the C # /. Net structure for outputting numbers with digits other than 0-9 (or parsing support).
. ( / separtor/currency), 0-9 String.Replace , , String.Join.
var converted = String.Join("", 123490.ToString().Select(c => "٠١٢٣٤٥٦٧٨٩"[c-'0']));