private static void AddIrregularRule(string singular, string plural)
{
AddPluralRule(String.Concat("(", singular[0], ")", singular.Substring(1), "$"),
String.Concat("$1", plural.Substring(1)));
AddSingularRule(String.Concat("(", plural[0], ")", plural.Substring(1), "$"),
String.Concat("$1", singular.Substring(1)));
}