リソースファイルの国際化対応 - java.util.ResourceBundle

menu.file = File
menu.edit = Edit

menu.file = ファイル
menu.edit = 編集

ResourceBundle#getBundle(String baseName)
ResourceBundle#getBundle(String baseName, Locale locale)

ResourceBundle resource = ResourceBundle.getBundle("Application");

ResourceBundle resource = ResourceBundle.getBundle("com.test.Application");

ResourceBundle resource = ResourceBundle.getBundle("com.test.Application", Locale.JAPANESE);

ResourceBundle#getString(String key)

ResourceBundle#getStringArray(String key)

package com.test;

import java.util.Enumeration;
import java.util.Locale;
import java.util.ResourceBundle;

public class TestProperties  {
    public static void main(String []args) {
        //com.test.*というパッケージのクラス（TestProperties.class）ファイルと同じディレクトリに配置してください 
        String resourceFile = "com.test.Application";

        System.out.println("---英語 Locale---");
    //Application.properties
        ResourceBundle resource = ResourceBundle.getBundle(resourceFile);

        testResourceBundle(resource);

        System.out.println("---日本語　Locale.JAPANESE---");

    //Application_ja.properties
        resource = ResourceBundle.getBundle(resourceFile, Locale.JAPANESE);

        testResourceBundle(resource);
    }
    
    private static void testResourceBundle(ResourceBundle resource) {
        String menuFile = resource.getString("menu.file");
        System.out.println("menu.file" + menuFile);

        String menuEdit = resource.getString("menu.edit");
        System.out.println("menu.edit" + menuEdit);
    }
}