dependencies: 
    flutter_localizations: 
        sdk: flutter 
dev_dependencies:
    gen_lang: 0.1.3

pub run gen_lang:generate

|--- lib 
|--- res 
     |--- string 
         |--- string_en.json 
         |--- string_zh_TW.json 
         |--- string_ja.json 

{ 
    "simpleMessage": "This is a simple Message"
}

{
    "messageWithParams": "Hi ${yourName}, Welcome you!"
}

{ 
    "pluralMessageZero": "Hi ${interviewerName}, I have no working experience.", 
    "pluralMessageOne": "Hi ${interviewerName}, I have one year working experience.", 
    "pluralMessageTwo": "Hi ${interviewerName}, I have two years of working experience.", 
    "pluralMessageFew": "Hi ${interviewerName}, I have few years of working experience.", 
    "pluralMessageMany": "Hi ${interviewerName}, I worked for a long time.", 
    "pluralMessagePOther": "Hi ${interviewerName}, I have ${howMany} years of working experience."
}

{ 
    "genderMessageMale": "Hi ${name}, He is boy.", 
    "genderMessageFemale": "Hi ${name}, She is girl", 
    "genderMessageGOther": "Hi ${name}, he/she is boy/girl." 
}

import 'package:gen_lang_example/generated/i18n.dart';
...
MaterialApp(
      localizationsDelegates: [
        S.delegate,
        GlobalMaterialLocalizations.delegate,
        GlobalWidgetsLocalizations.delegate
      ],
      supportedLocales: S.delegate.supportedLocales,
      
      ...
      ...
        S.of(context).simpleMessage; // Simple Message 
        S.of(context).messageWithParams('developer'); // Message with parameters
        S.of(context).pluralMessage(10, 'King Wu'); // Plural Message with parameters
        S.of(context).genderMessage('male', 'King Wu'); // Gender Message with parameters

cd example
pub run gen_lang:generate