private static void addSpecificTextField(string userField, string language) { if (language == null) { throw new ArgumentNullException(nameof(language)); } UserFields.Add(userField); LocalizedFields.Add(userField); userField = userField.ToLowerInvariant(); var localized = GetLocalizedField(userField, language); _textFields.Add(localized); DisplayFieldByIndexField.Add(localized, userField); }