Учебник по Java i18n (интернационализация) и локализация

<ResouceBundleName>_<language_code>_<country_code>

menu.addCity = Add a new visited city.

menu.chooseAction = Choose an action:

menu.removeCity = Remove city from the tracker.

menu.changeLocale = Change the localization of the app.

menu.exit = Exit the app.

menu.editCity = Edit an existing city.

-> returns user’s default locale.

Using the system’s default localization on the app’s startup is a good practice. This method provides the user’s default locale, which you can use to load strings from ResourceBundle without the user even thinking about it.



```(String language_tag)```

 -> returns Locale for the language.

As you have already noticed, each Resource Bundle can be created for specific language tags. Sometimes you may need to differentiate between Australian English (en_AU) and American English (en_US) - so you can specify it using this method.



 ```(Locale.getAvailableLocales()```

-> returns an array of all installed locales.

We use this method when we want to know which locales are installed on the user’s JVM. You parse the list - you know what to serve to the user.

### Dates and Numbers

As I mentioned earlier, different countries may have different ways of presenting Dates and Numbers. Let's assume we have 1 million. In English, it should be formatted as 1,000,000; however, in German, it should be 1.000.000.

To format numbers, Locale-aware creates an instance of NumberFormat class:

-> 1,000,000

-> 1.000.000

Same thing for dates. To format a date in Java, all you need to do is create an instance of DateFormat class:

-> Aug 7, 2022

-> 07.08.2022

The best part is instead of hard-coding the locale, we can use the user’s locale to format everything according to their culture!


## Context

So, you build the app and have all strings in English. Here’s the time you invite translators to your project. A lot of different people will look at the strings you wrote. How to build our resources so they will be translatable?

The concept of context plays a huge role in localization. Without it, some text may be translated poorly, but not because of the translator. Complex resources must have context attached!

If you name a string “string1,” - the translator will have no idea what this string’s for. Here’s a <a href="https://blog.crowdin.com/2019/11/05/no-context-no-quality-give-translators-context-to-get-better-translations/" target="_blank">little reading material</a>
 on why it’s crucial.

Long story short: be sure to correctly name all your strings in the .properties files so that people can know the context of it.


## Java i18n Application Example

We have talked about internalization only in theory. Let’s get to the point with our tutorial, where we will use all our new knowledge.

This tutorial will help to create a light Java project and implement internalization. All the project files will be available to fork <a href="https://github.com/danielsutts/i18n-with-Crowdin" target="_blank">here</a>.

### App Overview:

Our application is a small city visit tracker. I’ll call it simple - City Visit Tracker. The user enters their name and is presented with a few actions:

1.  Add a new city to the list.   
2.  Remove a city from the list.
3.  Edit an already added city (we all had this problem remembering the dates, didn’t we?).    
4.  Change the localization of the app.
5.  And, finally, exit the app.

I will use <a href="https://crowdin.com/on-demand-demo" target="_blank">Crowdin</a> for the translation of my resources. Using Crowdin - later in the tutorial.

First things first, let’s define the Client class.



```javascript

public class Client {
   private Locale userLocale;
   private final String username;
   private Map<City, Date> visitedCities;
   public Client(Locale userLocale, String username) {
       this.userLocale = userLocale;
       this.username = username;
   }
   public Locale getUserLocale() {
       return userLocale;
   }
   public void setUserLocale(Locale userLocale) {
       this.userLocale = userLocale;
   }
   public String getUsername() {
       return username;
   }  
   public void addCity(City city, Date dateVisited) {
       this.visitedCities.put(city, dateVisited);
   }
   public void removeCity(City city, Date dateVisited) {
       this.visitedCities.remove(city, dateVisited);
   }
}

public class City {
   private final Locale cityLocale;
   private final String cityName;
   private final String cityCountry;
   public City(Locale cityLocale, String cityName, String cityCountry) {
       this.cityLocale = cityLocale;
       this.cityName = cityName;
       this.cityCountry = cityCountry;
   }
}

menu.printAll = Print all cities.

menu.addCity = Add a new visited city.

menu.chooseAction = Choose an action:

menu.removeCity = Remove city from the tracker.

menu.changeLocale = Change the localization of the app.

menu.exit = Exit the app.

menu.editCity = Edit an existing city.

word.yes = Yes

word.no = No

word.city = City

word.date = Date

And here are all the messages we are going to use in our application:

message.welcome = Welcome to City Visit Tracker!

message.hello = Hello,

message.enterYourName = Enter your name:

message.addCity = Add a new city!

message.addCityName = Enter the city name:

message.addCityDate = Enter the city visited date

message.saved = Successfully saved a new city!

message.cityDeleted = Successfully deleted a city!

message.cityEdited = Successfully edited a city!

message.forExample = for example:

message.noChanges = No changes will be applied.

message.chooseLocale = Choose one of available languages:

message.tryAgain = Try again.

message.noCities = No cities saved yet!

message.chooseDelete = Choose a city to delete.

message.chooseEdit = Choose a city to edit.

message.newCityName = Enter a new city name

message.newCityDate = Enter a new city visited date

private static void changeLocale() {   System.out.println(userResourceBundle.getString("message.chooseLocale"));
   System.out.println(Arrays.toString(locales));
   Scanner scanner = new Scanner(System.in);
   String newLocale = scanner.nextLine();
   try {
       userResourceBundle = ResourceBundle.getBundle("resources/MessageBundle", new Locale(newLocale));
   } catch (MissingResourceException e) {
      System.out.println(userResourceBundle.getString("message.tryAgain"));
       changeLocale();
   }
}

private static void menu() {
   Scanner scanner = new Scanner(System.in);
   // Print out the menu
   System.out.println(userResourceBundle.getString("menu.chooseAction"));
   System.out.println("0 - " + userResourceBundle.getString("menu.printAll"));
   System.out.println("1 - " + userResourceBundle.getString("menu.addCity"));
   System.out.println("2 - " + userResourceBundle.getString("menu.removeCity"));
   System.out.println("3 - " + userResourceBundle.getString("menu.editCity"));
   System.out.println("4 - " + userResourceBundle.getString("menu.changeLocale"));
   System.out.println("5 - " + userResourceBundle.getString("menu.exit"));
   String answer = scanner.nextLine();
…
   // If Menu Action is "Add City"
   if (answer.equals("1")) {
       try{
           addCity();
       } catch (Exception ex) {
     System.out.println(userResourceBundle.getString("message.noChanges"));       System.out.println(userResourceBundle.getString("message.tryAgain"));
       }
       menu();
   }


…

private static void addCity() throws ParseException {
   // Take user's input
   // Create a new City instance to fill it in
   Scanner scanner = new Scanner(System.in);
   City newCity = new City();
   // Add the user's locale to the City instance
   newCity.setCityLocale(userResourceBundle.getLocale());
   // Print out the city name prompt and set the new name
   System.out.println(userResourceBundle.getString("message.addCity"));
   System.out.print(userResourceBundle.getString("message.addCityName"));
   newCity.setCityName(scanner.nextLine());
   // Print out the date prompt and set the new date
   System.out.print(userResourceBundle.getString("message.addCityDate") + ' ');
   // Here, we transform the input data according to the user's locale
   // and save it as usual Date class
   DateFormat df = DateFormat.getDateInstance(DateFormat.DEFAULT, userResourceBundle.getLocale());
   System.out.println('(' + userResourceBundle.getString("message.forExample") + ' ' + pdf.format(new Date()) + ')');
   Date newDate = df.parse(scanner.nextLine());
   newCity.setVisitedDate(newDate);
   repo.addCity(newCity);
   // Tell user we saved a new city!
   System.out.println(userResourceBundle.getString("message.saved"));
}

protected static ResourceBundle userResourceBundle;

private static final String[] locales = new String[]{"en_US", "pl_PL", "uk_UA"};

private static final CityRepository repo = new CityRepository();

public static void main(String[] args) {
   // Get user's default locale
   // Load ResourceBundle for the locale
   Locale locale = Locale.getDefault();
   userResourceBundle = ResourceBundle.getBundle("resources/MessageBundle", locale);

   Scanner scanner = new Scanner(System.in);
   System.out.println(userResourceBundle.getString("message.welcome"));
   System.out.print(userResourceBundle.getString("message.enterYourName") + ' ');

   String name = scanner.nextLine();
   Client client = new Client(locale, name);

   System.out.println(userResourceBundle.getString("message.hello") + ' ' + client.getUsername() + "!");

   menu();
}