function GregorianCalendar(language) {
        this.local = this.regionalOptions[language] || this.regionalOptions[""];
      }
Check that a candidate date is from the same calendar and is valid.
            @memberof BaseCalendar
            @private
            @param year {CDate|number} The date to validate or the year to validate.
            @param [month] {number} The month to validate.
            @param [day] {number} The day to validate.
            @param error {string} Rrror message if invalid.
            @throws Error if different calendars used or invalid date.