title: Android Adding "values-en" folder causes "Couldn't resolve resource" warning
body: <p>I have the next problem:</p>
  
  <p>When I add a new folder called <em>"values-en"</em> and I move the <em>strings.xml</em> file from the default folder <em>"values"</em> to that <em>"values-en"</em>, I always get the next error:</p>
  
  <p><code>Couldn't resolve resource @string/my_string</code></p>
  
  <p>I have cleaned the project and refresh and the warning is always there.</p>
  
  <p>Is there any restriction where I must always have a strings.xml in the device folder "values"?</p>
  
  <p>Someone has experimented the same?</p>
  
  <p>Thanks in advance</p>