Fix #648: allow using "old" (e.g. pre-3.0.4) plural rules evaluation

Add forcePluralCaseFallback option to force evaluation of fallback
plural rules, i.e.

* forcePluralCaseFallback: false
Default behavior, will use "zero" rule for 0 only if the language
is set to do so (e.g. for "lt" but not for "en").

* forcePluralCaseFallback: true
Force using "zero" rule for 0 even if the language doesn't use it
by default (e.g. "en"). If "zero" localization for that string
doesn't exist, "other" is still used as fallback.

example/lib/main.dart

@@ -23,6 +23,7 @@ void main() async {
     // startLocale: Locale('de', 'DE'),
     // saveLocale: false,
     // useOnlyLangCode: true,
+    forcePluralCaseFallback: true,
 
     // optional assetLoader default used is RootBundleAssetLoader which uses flutter's assetloader
     // install easy_localization_loader for enable custom loaders

example/resources/langs/en-US.json

@@ -11,12 +11,10 @@
         }
     },
     "clicked": {
-        "zero": "You clicked {} times!",
-        "one": "You clicked {} time!",
-        "two": "You clicked {} times!",
-        "few": "You clicked {} times!",
-        "many": "You clicked {} times!",
-        "other": "You clicked {} times!"
+        "zero": "You didn't click yet!",
+        "few": "You clicked a few times ({})!",
+        "many": "You clicked many times ({})!",
+        "other": "You clicked {} time(s)!"
     },
     "amount": {
         "zero": "Your amount : {} ",

lib/src/easy_localization_app.dart

@@ -63,6 +63,21 @@ class EasyLocalization extends StatefulWidget {
   /// ```
   final bool useFallbackTranslationsForEmptyResources;
 
+  /// Force use of plural strings for all languages. This will still fallback
+  /// to "other" if the specific rule isn't defined.
+  /// @Default value false
+  /// Example:
+  /// ```
+  /// // Default behavior, will use "zero" rule for 0 only if the language
+  /// // is set to do so (e.g. for "lt" but not for "en").
+  /// forcePluralCaseFallback: false
+  /// // Force using "zero" rule for 0 even if the language doesn't use it
+  /// // by default (e.g. "en"). If "zero" localization for that string
+  /// // doesn't exist, "other" is still used as fallback.
+  /// forcePluralCaseFallback: true
+  /// ```
+  final bool forcePluralCaseFallback;
+
   /// Path to your folder with localization files.
   /// Example:
   /// ```dart
@@ -117,6 +132,7 @@ class EasyLocalization extends StatefulWidget {
     this.useOnlyLangCode = false,
     this.useFallbackTranslations = false,
     this.useFallbackTranslationsForEmptyResources = false,
+    this.forcePluralCaseFallback = false,
     this.assetLoader = const RootBundleAssetLoader(),
     this.extraAssetLoaders,
     this.saveLocale = true,
@@ -198,6 +214,7 @@ class _EasyLocalizationState extends State<EasyLocalization> {
         supportedLocales: widget.supportedLocales,
         useFallbackTranslationsForEmptyResources:
             widget.useFallbackTranslationsForEmptyResources,
+        forcePluralCaseFallback: widget.forcePluralCaseFallback,
       ),
     );
   }
@@ -243,6 +260,7 @@ class _EasyLocalizationProvider extends InheritedWidget {
 
   /// Get fallback locale
   Locale? get fallbackLocale => parent.fallbackLocale;
+
   // Locale get startLocale => parent.startLocale;
 
   /// Change app locale
@@ -278,12 +296,14 @@ class _EasyLocalizationDelegate extends LocalizationsDelegate<Localization> {
   final List<Locale>? supportedLocales;
   final EasyLocalizationController? localizationController;
   final bool useFallbackTranslationsForEmptyResources;
+  final bool forcePluralCaseFallback;
 
   ///  * use only the lang code to generate i18n file path like en.json or ar.json
   // final bool useOnlyLangCode;
 
   _EasyLocalizationDelegate({
     required this.useFallbackTranslationsForEmptyResources,
+    this.forcePluralCaseFallback = false,
     this.localizationController,
     this.supportedLocales,
   }) {
@@ -306,6 +326,7 @@ class _EasyLocalizationDelegate extends LocalizationsDelegate<Localization> {
       fallbackTranslations: localizationController!.fallbackTranslations,
       useFallbackTranslationsForEmptyResources:
           useFallbackTranslationsForEmptyResources,
+      forcePluralCaseFallback: forcePluralCaseFallback,
     );
     return Future.value(Localization.instance);
   }

lib/src/localization.dart

@@ -20,11 +20,14 @@ class Localization {
   };
 
   bool _useFallbackTranslationsForEmptyResources = false;
+  bool _forcePluralCaseFallback = false;
 
   Localization();
 
   static Localization? _instance;
+
   static Localization get instance => _instance ?? (_instance = Localization());
+
   static Localization? of(BuildContext context) =>
       Localizations.of<Localization>(context, Localization);
 
@@ -33,12 +36,14 @@ class Localization {
     Translations? translations,
     Translations? fallbackTranslations,
     bool useFallbackTranslationsForEmptyResources = false,
+    bool forcePluralCaseFallback = false,
   }) {
     instance._locale = locale;
     instance._translations = translations;
     instance._fallbackTranslations = fallbackTranslations;
     instance._useFallbackTranslationsForEmptyResources =
         useFallbackTranslationsForEmptyResources;
+    instance._forcePluralCaseFallback = forcePluralCaseFallback;
     return translations == null ? false : true;
   }
 
@@ -114,6 +119,9 @@ class Localization {
   }
 
   static PluralRule? _pluralRule(String? locale, num howMany) {
+    if (instance._forcePluralCaseFallback) {
+      return () => _pluralCaseFallback(howMany);
+    }
     startRuleEvaluation(howMany);
     return pluralRules[locale];
   }
@@ -139,11 +147,11 @@ class Localization {
     String? name,
     NumberFormat? format,
   }) {
-
     late String res;
 
     final pluralRule = _pluralRule(_locale.languageCode, value);
-    final pluralCase = pluralRule != null ? pluralRule() : _pluralCaseFallback(value);
+    final pluralCase =
+        pluralRule != null ? pluralRule() : _pluralCaseFallback(value);
 
     switch (pluralCase) {
       case PluralCase.ZERO:
@@ -186,7 +194,8 @@ class Localization {
     if (subKey == 'other') return _resolve('$key.other');
 
     final tag = '$key.$subKey';
-    var resource = _resolve(tag, logging: false, fallback: _fallbackTranslations != null);
+    var resource =
+        _resolve(tag, logging: false, fallback: _fallbackTranslations != null);
     if (resource == tag) {
       resource = _resolve('$key.other');
     }