title: Load messages files in MessageSouce from imported jar
body: <p>I have spring boot application using i18n that imports a jar file as a library.
  In jar library there are messages.properties files <code>messages.properties, messages_en.properties, ...</code> that I want to use.</p>
  
  <p>Problem is that <code>messages.properties</code> files from the library are not loaded and I can't use translations from them. </p>
  
  <p>I have MessageSource bean set up as bellow and I can't figure out what path should I add to access <code>messages.properties</code> files in the library. Now only messages.properties files from the main app are used</p>
  
  <pre><code>@Bean
      public MessageSource messageSource() {
          ReloadableResourceBundleMessageSource  messageSource = new ReloadableResourceBundleMessageSource();
          messageSource.setBasenames(
                  "classpath:messages", 
  //              " path to messages in library ?" 
          );
          messageSource.setUseCodeAsDefaultMessage(true);
          messageSource.setDefaultEncoding("UTF-8");
          return messageSource;
      }
  </code></pre>
  
  <p>Messages in the library were added to resources, so they are in the base folder of the jar
  <img src="https://i.stack.imgur.com/kp63U.png" alt="library_structure_picture"></p>