title: Java 8 streams - map element to pair of elements
body: <p>I have a stream of elements. I want to map each element to two different elements of the same type so that my stream will be two times longer in consequence.
  I did this by concatenating two streams, but I'm wondering is it possible to do this simpler?
  What I've done so far:</p>
  
  <pre><code>private List&lt;String&gt; getTranslationFilesNames() {
  return Stream.concat(SUPPORTED_LANGUAGES.stream()
                  .map(lang -&gt; PATH_TO_FILES_WITH_TRANSLATIONS_1 + lang + FILE_EXTENSION),
          SUPPORTED_LANGUAGES.stream()
                  .map(lang -&gt; PATH_TO_FILES_WITH_TRANSLATIONS_2 + lang + FILE_EXTENSION))
          .collect(Collectors.toList());
  }
  </code></pre>
  
  <p>I don't find this solution very elegant. Is there better approach to achieve the same effect?</p>