Invalid argument(s): Invalid locale "en_US"

Question

I successfully created my newly supported language which is 'rw' (Rwandan language), and you can change the state of language but every time I restart the app while in my language('rw') state, I get the following error, does anyone know how to resolve this issue?

The following ArgumentError was thrown building:
Invalid argument(s): Invalid locale "en_US"

When the exception was thrown, this was the stack
#0      _throwLocaleError
package:intl/src/intl_helpers.dart:177
#1      verifiedLocale
package:intl/src/intl_helpers.dart:171
#2      verifiedLocale
package:intl/src/intl_helpers.dart:156
#3      new DateFormat
package:intl/…/intl/date_format.dart:266
#4      new DateFormat.yMEd
package:intl/…/intl/date_format.dart:478

Here is my rw_intl.dart file

import 'dart:async';

import 'package:intl/intl.dart' as intl;
import 'package:intl/date_symbols.dart' as intl;
import 'package:intl/date_symbol_data_custom.dart' as date_symbol_data_custom;
import 'package:flutter/foundation.dart';
import 'package:flutter/material.dart';
import 'package:flutter_localizations/flutter_localizations.dart';

/// A custom set of date patterns for the `rw` locale.
///
/// These are not accurate and are just a clone of the date patterns for the
/// `no` locale to demonstrate how one would write and use custom date patterns.
const rwLocaleDatePatterns = {
  'd': 'd.',
  'E': 'ccc',
  'EEEE': 'cccc',
  'LLL': 'LLL',
  'LLLL': 'LLLL',
  'M': 'L.',
  'Md': 'd.M.',
  'MEd': 'EEE d.M.',
  'MMM': 'LLL',
  'MMMd': 'd. MMM',
  'MMMEd': 'EEE d. MMM',
  'MMMM': 'LLLL',
  'MMMMd': 'd. MMMM',
  'MMMMEEEEd': 'EEEE d. MMMM',
  'QQQ': 'QQQ',
  'QQQQ': 'QQQQ',
  'y': 'y',
  'yM': 'M.y',
  'yMd': 'd.M.y',
  'yMEd': 'EEE d.MM.y',
  'yMMM': 'MMM y',
  'yMMMd': 'd. MMM y',
  'yMMMEd': 'EEE d. MMM y',
  'yMMMM': 'MMMM y',
  'yMMMMd': 'd. MMMM y',
  'yMMMMEEEEd': 'EEEE d. MMMM y',
  'yQQQ': 'QQQ y',
  'yQQQQ': 'QQQQ y',
  'H': 'HH',
  'Hm': 'HH:mm',
  'Hms': 'HH:mm:ss',
  'j': 'HH',
  'jm': 'HH:mm',
  'jms': 'HH:mm:ss',
  'jmv': 'HH:mm v',
  'jmz': 'HH:mm z',
  'jz': 'HH z',
  'm': 'm',
  'ms': 'mm:ss',
  's': 's',
  'v': 'v',
  'z': 'z',
  'zzzz': 'zzzz',
  'ZZZZ': 'ZZZZ',
};

/// A custom set of date symbols for the `rw` locale.
///
/// These are not accurate and are just a clone of the date symbols for the
/// `no` locale to demonstrate how one would write and use custom date symbols.
const rwDateSymbols = {
  'NAME': 'rw',
  'ERAS': <dynamic>[
    'm.Kr.',
    'n.Kr.',
  ],
  'ERANAMES': <dynamic>[
    'mbere ya Kristu',
    'nyuma ya Kristu',
  ],
  'NARROWMONTHS': <dynamic>[
    'M',
    'G',
    'W',
    'M',
    'G',
    'K',
    'N',
    'K',
    'N',
    'U',
    'U',
    'U',
  ],
  'STANDALONENARROWMONTHS': <dynamic>[
    'M',
    'G',
    'W',
    'M',
    'G',
    'K',
    'N',
    'K',
    'N',
    'U',
    'U',
    'U',
  ],
  'MONTHS': <dynamic>[
    'Mutarama',
    'Gashyantare',
    'Werurwe',
    'Mata',
    'Gicurasi',
    'Kamena',
    'Nyakanga',
    'Kanama',
    'Nzeli',
    'Ukwakira',
    'Ugushyingo',
    'Ukuboza',
  ],
  'STANDALONEMONTHS': <dynamic>[
    'Mutarama',
    'Gashyantare',
    'Werurwe',
    'Mata',
    'Gicurasi',
    'Kamena',
    'Nyakanga',
    'Kanama',
    'Nzeli',
    'Ukwakira',
    'Ugushyingo',
    'Ukuboza',
  ],
  'SHORTMONTHS': <dynamic>[
    'Mut.',
    'Gas.',
    'Wer.',
    'Mat.',
    'Gic.',
    'Kam.',
    'Nya.',
    'Kan.',
    'Nze.',
    'Ukw.',
    'Ugu.',
    'Uku.',
  ],
  'STANDALONESHORTMONTHS': <dynamic>[
    'Mut.',
    'Gas.',
    'Wer.',
    'Mat.',
    'Gic.',
    'Kam.',
    'Nya.',
    'Kan.',
    'Nze.',
    'Ukw.',
    'Ugu.',
    'Uku.',
  ],
  'WEEKDAYS': <dynamic>[
    'ku cyumweru',
    'ku wa mbere',
    'ku wa kabiri',
    'ku wa gatatu',
    'ku wa kane',
    'ku wa gatanu',
    'ku wa gatandatu',
  ],
  'STANDALONEWEEKDAYS': <dynamic>[
    'ku cyumweru',
    'ku wa mbere',
    'ku wa kabiri',
    'ku wa gatatu',
    'ku wa kane',
    'ku wa gatanu',
    'ku wa gatandatu',
  ],
  'SHORTWEEKDAYS': <dynamic>[
    'cyumwer.',
    'mbere.',
    'kabiri.',
    'gatatu.',
    'kane.',
    'gatanu.',
    'gatandat.',
  ],
  'STANDALONESHORTWEEKDAYS': <dynamic>[
    'cyumwer.',
    'mbere.',
    'kabiri.',
    'gatatu.',
    'kane.',
    'gatanu.',
    'gatandat.',
  ],
  'NARROWWEEKDAYS': <dynamic>[
    'C',
    'M',
    'K',
    'G',
    'K',
    'G',
    'G',
  ],
  'STANDALONENARROWWEEKDAYS': <dynamic>[
    'C',
    'M',
    'K',
    'G',
    'K',
    'G',
    'G',
  ],
  'SHORTQUARTERS': <dynamic>[
    'K1',
    'K2',
    'K3',
    'K4',
  ],
  'QUARTERS': <dynamic>[
    'kimwe cya kane',
    'bibiri bya kane',
    'bitatu bya kane',
    'bine bya kane',
  ],
  'AMPMS': <dynamic>[
    'za mu gitondo',
    'z\' umugoroba ',
  ],
  'DATEFORMATS': <dynamic>[
    'EEEE d. MMMM y',
    'd. MMMM y',
    'd. MMM y',
    'dd.MM.y',
  ],
  'TIMEFORMATS': <dynamic>[
    'HH:mm:ss zzzz',
    'HH:mm:ss z',
    'HH:mm:ss',
    'HH:mm',
  ],
  'AVAILABLEFORMATS': null,
  'FIRSTDAYOFWEEK': 0,
  'WEEKENDRANGE': <dynamic>[
    5,
    6,
  ],
  'FIRSTWEEKCUTOFFDAY': 3,
  'DATETIMEFORMATS': <dynamic>[
    '{1} {0}',
    '{1} \'kl\'. {0}',
    '{1}, {0}',
    '{1}, {0}',
  ],
};

class _RwMaterialLocalizationsDelegate
    extends LocalizationsDelegate<MaterialLocalizations> {
  const _RwMaterialLocalizationsDelegate();

  @override
  bool isSupported(Locale locale) => locale.languageCode == 'rw';

  @override
  Future<MaterialLocalizations> load(Locale locale) async {
    final String localeName = intl.Intl.canonicalizedLocale(locale.toString());

    // The locale (in this case `rw`) needs to be initialized into the custom
    // date symbols and patterns setup that Flutter uses.
    date_symbol_data_custom.initializeDateFormattingCustom(
      locale: localeName,
      patterns: rwLocaleDatePatterns,
      symbols: intl.DateSymbols.deserializeFromMap(rwDateSymbols),
    );

    return SynchronousFuture<MaterialLocalizations>(
      RwMaterialLocalizations(
        localeName: localeName,
        // The `intl` library's NumberFormat class is generated from CLDR data
        // (see https://github.com/dart-lang/intl/blob/master/lib/number_symbols_data.dart).
        // Unfortunately, there is no way to use a locale that isn't defined in
        // this map and the only way to work around this is to use a listed
        // locale's NumberFormat symbols. So, here we use the number formats
        // for 'en_US' instead.
        decimalFormat: intl.NumberFormat('#,##0.###', 'en_US'),
        twoDigitZeroPaddedFormat: intl.NumberFormat('00', 'en_US'),
        // DateFormat here will use the symbols and patterns provided in the
        // `date_symbol_data_custom.initializeDateFormattingCustom` call above.
        // However, an alternative is to simply use a supported locale's
        // DateFormat symbols, similar to NumberFormat above.
        fullYearFormat: intl.DateFormat('y', localeName),
        compactDateFormat: intl.DateFormat('yMd', localeName),
        shortDateFormat: intl.DateFormat('yMMMd', localeName),
        mediumDateFormat: intl.DateFormat('EEE, MMM d', localeName),
        longDateFormat: intl.DateFormat('EEEE, MMMM d, y', localeName),
        yearMonthFormat: intl.DateFormat('MMMM y', localeName),
        shortMonthDayFormat: intl.DateFormat('MMM d', localeName),
      ),
    );
  }

  @override
  bool shouldReload(_RwMaterialLocalizationsDelegate old) => false;
}

/// A custom set of localizations for the 'rw' locale. In this example, only
/// the value for openAppDrawerTooltip was modified to use a custom message as
/// an example. Everything else uses the American English (en_US) messages
/// and formatting.
class RwMaterialLocalizations extends GlobalMaterialLocalizations {
  const RwMaterialLocalizations({
    String localeName = 'rw',
    @required intl.DateFormat fullYearFormat,
    @required intl.DateFormat compactDateFormat,
    @required intl.DateFormat shortDateFormat,
    @required intl.DateFormat mediumDateFormat,
    @required intl.DateFormat longDateFormat,
    @required intl.DateFormat yearMonthFormat,
    @required intl.DateFormat shortMonthDayFormat,
    @required intl.NumberFormat decimalFormat,
    @required intl.NumberFormat twoDigitZeroPaddedFormat,
  }) : super(
          localeName: localeName,
          fullYearFormat: fullYearFormat,
          compactDateFormat: compactDateFormat,
          shortDateFormat: shortDateFormat,
          mediumDateFormat: mediumDateFormat,
          longDateFormat: longDateFormat,
          yearMonthFormat: yearMonthFormat,
          shortMonthDayFormat: shortMonthDayFormat,
          decimalFormat: decimalFormat,
          twoDigitZeroPaddedFormat: twoDigitZeroPaddedFormat,
        );

  @override
  String get moreButtonTooltip => r'Ibindi';

  @override
  String get aboutListTileTitleRaw => r'Ibijyanye $applicationName';

  @override
  String get alertDialogLabel => r'Imenyesha';

  @override
  String get anteMeridiemAbbreviation => r'AM';

  @override
  String get backButtonTooltip => r'Inyuma';

  @override
  String get cancelButtonLabel => r'HAGARIKA';

  @override
  String get closeButtonLabel => r'FUNGA';

  @override
  String get closeButtonTooltip => r'Funga';

  @override
  String get collapsedIconTapHint => r'Agura';

  @override
  String get continueButtonLabel => r'KOMEZA';

  @override
  String get copyButtonLabel => r'KOPIYA';

  @override
  String get cutButtonLabel => r'KATINGA';

  @override
  String get deleteButtonTooltip => r'Siba';

  @override
  String get dialogLabel => r'Ikiganiro';

  @override
  String get drawerLabel => r'Ibikubiyemo';

  @override
  String get expandedIconTapHint => r'Gabanya';

  @override
  String get hideAccountsLabel => r'Hishya konte';

  @override
  String get licensesPageTitle => r'Licenses';

  @override
  String get modalBarrierDismissLabel => r'Dismiss';

  @override
  String get nextMonthTooltip => r'Ukwezi gutaha';

  @override
  String get nextPageTooltip => r'Paji ikurikira';

  @override
  String get okButtonLabel => r'KOMEZA';

  @override
  // A custom drawer tooltip message.
  String get openAppDrawerTooltip => r'Custom Navigation Menu Tooltip';

  @override
  String get pageRowsInfoTitleRaw => r'$firstRow–$lastRow of $rowCount';

  @override
  String get pageRowsInfoTitleApproximateRaw =>
      r'$firstRow–$lastRow of about $rowCount';

  @override
  String get pasteButtonLabel => r'PASTE';

  @override
  String get popupMenuLabel => r'Popup menu';

  @override
  String get postMeridiemAbbreviation => r'PM';

  @override
  String get previousMonthTooltip => r'Ukwezi gushize';

  @override
  String get previousPageTooltip => r'Paji ibanza';

  @override
  String get refreshIndicatorSemanticLabel => r'Refresh';

  @override
  String get remainingTextFieldCharacterCountFew => null;

  @override
  String get remainingTextFieldCharacterCountMany => null;

  @override
  String get remainingTextFieldCharacterCountOne => r'inyuguti imwe isigaye';

  @override
  String get remainingTextFieldCharacterCountOther =>
      r'inyuguti $remainingCount zisigaye';

  @override
  String get remainingTextFieldCharacterCountTwo => null;

  @override
  String get remainingTextFieldCharacterCountZero => r'Nta nyuguti isigaye';

  @override
  String get reorderItemDown => r'Manuka';

  @override
  String get reorderItemLeft => r'Jya ibumoso';

  @override
  String get reorderItemRight => r'Jya iburyo';

  @override
  String get reorderItemToEnd => r'Manuka ahahera';

  @override
  String get reorderItemToStart => r'Zamuka ahabanza';

  @override
  String get reorderItemUp => r'Zamuka';

  @override
  String get rowsPerPageTitle => r'Rows per page:';

  @override
  ScriptCategory get scriptCategory => ScriptCategory.englishLike;

  @override
  String get searchFieldLabel => r'Ishakiro';

  @override
  String get selectAllButtonLabel => r'HITAMO BYOSE';

  @override
  String get selectedRowCountTitleFew => null;

  @override
  String get selectedRowCountTitleMany => null;

  @override
  String get selectedRowCountTitleOne => r'1 item selected';

  @override
  String get selectedRowCountTitleOther => r'$selectedRowCount items selected';

  @override
  String get selectedRowCountTitleTwo => null;

  @override
  String get selectedRowCountTitleZero => r'No items selected';

  @override
  String get showAccountsLabel => r'Garagaza konte';

  @override
  String get showMenuTooltip => r'Garagaza Ibikubiyemo';

  @override
  String get signedInLabel => r'Winjiye';

  @override
  String get tabLabelRaw => r'Tab $tabIndex of $tabCount';

  @override
  TimeOfDayFormat get timeOfDayFormatRaw => TimeOfDayFormat.h_colon_mm_space_a;

  @override
  String get timePickerHourModeAnnouncement => r'Hitamo amasaha';

  @override
  String get timePickerMinuteModeAnnouncement => r'Hitamo iminota';

  @override
  String get viewLicensesButtonLabel => r'VIEW LICENSES';

  @override
  List<String> get narrowWeekdays =>
      const <String>['C', 'M', 'K', 'G', 'K', 'G', 'G'];

  @override
  int get firstDayOfWeekIndex => 0;

  static const LocalizationsDelegate<MaterialLocalizations> delegate =
      _RwMaterialLocalizationsDelegate();

  @override
  String get calendarModeButtonLabel => r'Jya kuri kalendari';

  @override
  String get dateHelpText => r'mm/dd/yyyy';

  @override
  String get dateInputLabel => r'Injiza itariki';

  @override
  String get dateOutOfRangeLabel => r'Out of range.';

  @override
  String get datePickerHelpText => r'HITAMO ITARIKI';

  @override
  String get dateRangeEndDateSemanticLabelRaw => r'Itariki ihera $fullDate';

  @override
  String get dateRangeEndLabel => r'Itariki ihera';

  @override
  String get dateRangePickerHelpText => 'HITAMO INTERA';

  @override
  String get dateRangeStartDateSemanticLabelRaw => 'Itariki ibanza \$fullDate';

  @override
  String get dateRangeStartLabel => 'Itariki ibanza';

  @override
  String get dateSeparator => '/';

  @override
  String get dialModeButtonLabel => 'Switch to dial picker mode';

  @override
  String get inputDateModeButtonLabel => 'Switch to input';

  @override
  String get inputTimeModeButtonLabel => 'Switch to text input mode';

  @override
  String get invalidDateFormatLabel => 'Invalid format.';

  @override
  String get invalidDateRangeLabel => 'Invalid range.';

  @override
  String get invalidTimeLabel => 'Enter a valid time';

  @override
  String get licensesPackageDetailTextOther => '\$licenseCount licenses';

  @override
  String get saveButtonLabel => 'BIKA';

  @override
  String get selectYearSemanticsLabel => 'Hitamo umwaka';

  @override
  String get timePickerDialHelpText => 'HITAMO IGIHE';

  @override
  String get timePickerHourLabel => 'Isaha';

  @override
  String get timePickerInputHelpText => 'INJIZA GIHE';

  @override
  String get timePickerMinuteLabel => 'Umunota';

  @override
  String get unspecifiedDate => 'Itariki';

  @override
  String get unspecifiedDateRange => 'Date Range';
}

Here is my main.dart file

`locale: _locale,
supportedLocales: [
Locale('en'),
Locale('rw'),
],
localizationsDelegates: [
DemoLocalization.delegate,
GlobalMaterialLocalizations.delegate,
GlobalWidgetsLocalizations.delegate,
GlobalCupertinoLocalizations.delegate,
RwMaterialLocalizations.delegate,
],

        localeResolutionCallback: (deviceLocale, supportedLocales) {
          for (var locale in supportedLocales) {
            if (locale.languageCode == deviceLocale.languageCode) {
              return deviceLocale;
            }
          }
          return supportedLocales.first;
        },`

Answer 1

You need to add it to intl cache as well:

           ...
date_symbol_data_custom.initializeDateFormattingCustom(
      locale: localeName,
      patterns: rwLocaleDatePatterns,
      symbols: intl.DateSymbols.deserializeFromMap(rwDateSymbols),
    );


 date_symbol_data_custom.initializeDateFormattingCustom(
  locale: 'en_US',
  patterns: dateTimePatternMap()['en_US'],
  symbols: dateTimeSymbolMap()['en_US'],
);
        ...

Answer 2

supportedLocales: [
    Locale('en', 'Us'),    
],

Answer 3

The issue is that you have set supported locales to :

   supportedLocales: [
Locale('en'),
Locale('rw'),
],

Replace Locale('en') with Locale('en_US') as the error is suggesting . The reason you are getting the error is because your device locale is en_US and not en. Best approach would be to centralise your supported locales. If you have the intl plugin in your code editor (VS code or Android Studio) then you should have this generated folder (lib/generated/l10n.dart). In this file you will find a class called AppLocalizationDelegate in this class you will find a list of supportedLocales. In your main.dart call this list

import 'package:your_package_name_here/generated/l10n.dart';

supportedLocales: AppLocalizationDelegate().supportedLocales,