Internationalization (I18N) and Localization (L10N) in Java

Introduction

Internationalization (I18N) and Localization (L10N) are two important concepts for making software applications globally accessible. Internationalization is the process of designing an application so that it can be easily adapted to different languages and regions without engineering changes. Localization is the process of adapting the application to a specific language and region.

This tutorial demonstrates how to implement internationalization and localization in Java using ResourceBundle, Locale, and Properties files.

Step 1: Understanding ResourceBundle and Locale

In Java, the ResourceBundle class is used to store locale-specific objects. These objects can be strings, images, or other resources. The Locale class is used to define a region or language-specific setting (such as English in the US or French in Canada).

Example of ResourceBundle and Locale

          // ResourceBundle Example
      
          import java.util.*;
      
          public class I18nExample {
              public static void main(String[] args) {
                  // Create Locale for English in US
                  Locale locale = new Locale("en", "US");
      
                  // Get ResourceBundle for the locale
                  ResourceBundle messages = ResourceBundle.getBundle("MessagesBundle", locale);
      
                  // Access a message from the bundle
                  System.out.println(messages.getString("greeting"));
              }
          }
        

In this example:

• We create a Locale object representing the English language in the United States.
• We use ResourceBundle.getBundle() to load the properties file specific to that locale (in this case, MessagesBundle_en_US.properties).
• We retrieve a string from the resource bundle using messages.getString("greeting").

Step 2: Creating Properties Files for Different Locales

To enable localization, we create properties files that contain language-specific data. These files are loaded dynamically based on the user's locale.

Example: Creating Properties Files

          # MessagesBundle_en_US.properties (English - US)
          greeting=Hello!
      
          # MessagesBundle_fr_FR.properties (French - France)
          greeting=Bonjour!
      
          # MessagesBundle_es_ES.properties (Spanish - Spain)
          greeting=¡Hola!
        

In these property files:

• The keys are the same across all files (in this case, greeting).
• The values are language-specific and provide translations for the greeting message.

Step 3: Running the Example for Different Locales

Now, let's see how the program behaves for different locales.

Example Code to Handle Multiple Locales

          // ResourceBundle with Multiple Locales Example
      
          import java.util.*;
      
          public class I18nExample {
              public static void main(String[] args) {
                  // Locale for English in US
                  Locale localeUS = new Locale("en", "US");
                  ResourceBundle messagesUS = ResourceBundle.getBundle("MessagesBundle", localeUS);
                  System.out.println("US Greeting: " + messagesUS.getString("greeting"));
      
                  // Locale for French in France
                  Locale localeFR = new Locale("fr", "FR");
                  ResourceBundle messagesFR = ResourceBundle.getBundle("MessagesBundle", localeFR);
                  System.out.println("FR Greeting: " + messagesFR.getString("greeting"));
      
                  // Locale for Spanish in Spain
                  Locale localeES = new Locale("es", "ES");
                  ResourceBundle messagesES = ResourceBundle.getBundle("MessagesBundle", localeES);
                  System.out.println("ES Greeting: " + messagesES.getString("greeting"));
              }
          }
        

When you run this program, the output will vary based on the system's locale or the one you provide:

• For en_US, the output will be: Hello!
• For fr_FR, the output will be: Bonjour!
• For es_ES, the output will be: ¡Hola!

Step 4: Handling Fallback Mechanism

If there is no specific resource bundle for a particular locale, Java will fall back to the default locale (usually English). You can also provide a fallback resource bundle to ensure that your application doesn't fail when no specific localization is found.

Example of Fallback Mechanism

          // ResourceBundle with Fallback Example
      
          import java.util.*;
      
          public class I18nExample {
              public static void main(String[] args) {
                  // Locale for Italian (no specific resource bundle)
                  Locale localeIT = new Locale("it", "IT");
                  ResourceBundle messagesIT = ResourceBundle.getBundle("MessagesBundle", localeIT);
                  System.out.println("IT Greeting: " + messagesIT.getString("greeting")); // Falls back to default (English)
      
                  // Locale for German (no specific resource bundle)
                  Locale localeDE = new Locale("de", "DE");
                  ResourceBundle messagesDE = ResourceBundle.getBundle("MessagesBundle", localeDE);
                  System.out.println("DE Greeting: " + messagesDE.getString("greeting")); // Falls back to default (English)
              }
          }
        

In this example, if there is no MessagesBundle_it_IT.properties or MessagesBundle_de_DE.properties file, the program will fall back to the default language, which is English.

Step 5: Locale Sensitive Operations

Locale-sensitive operations such as formatting numbers, dates, and currencies are part of Java's internationalization capabilities. These operations are important to ensure that your application works correctly across different regions.

Example of Locale-Sensitive Formatting

          import java.text.*;
          import java.util.*;
      
          public class LocaleSensitiveExample {
              public static void main(String[] args) {
                  // Locale for French (France)
                  Locale localeFR = new Locale("fr", "FR");
                  NumberFormat currencyFormatFR = NumberFormat.getCurrencyInstance(localeFR);
                  double price = 1234.56;
                  System.out.println("Price in France: " + currencyFormatFR.format(price));
      
                  // Locale for US (United States)
                  Locale localeUS = new Locale("en", "US");
                  NumberFormat currencyFormatUS = NumberFormat.getCurrencyInstance(localeUS);
                  System.out.println("Price in US: " + currencyFormatUS.format(price));
              }
          }
        

In this example:

• We use NumberFormat.getCurrencyInstance() to format the price based on the locale.
• For the French locale, the price is displayed as "1 234,56 €".
• For the US locale, the price is displayed as "$1,234.56".

Conclusion

Internationalization and localization are crucial aspects of building global applications. Java provides powerful tools like ResourceBundle, Locale, and NumberFormat to handle various internationalization and localization tasks. In this tutorial, we:

• Learned how to use ResourceBundle and Locale to retrieve localized resources.
• Created multiple properties files for different languages.
• Explored how to handle fallback mechanisms when a specific resource is unavailable.
• Used Java's locale-sensitive formatting for dates, currencies, and numbers.