title: ResourceManager returning null for default culture
body: <p>I'm working on a Xamarin Forms app, using a .NET Standard library. I've used the <code>TranslateExtension</code> as mentioned in <a href="https://developer.xamarin.com/guides/xamarin-forms/advanced/localization/#Localizing_XAML" rel="nofollow noreferrer">the docs</a>. I've added three resource files:</p>
  
  <ul>
  <li><code>AppResources.resx</code> (with matching code-behind file, auto-generated)</li>
  <li><code>AppResources.nl.resx</code> (Dutch translations)</li>
  <li><code>AppResources.fr.resx</code> (English tranlations)</li>
  </ul>
  
  <p>When debugging the (UWP) app, I can't get the default culture (English) to be displayed. The following line returns null:</p>
  
  <pre><code>ResMgr.Value.GetString(Text, ci);
  </code></pre>
  
  <p>I've add some lines for debugging, and the other two languages do return the translated value:</p>
  
  <pre><code>ResMgr.Value.GetString(Text, new CultureInfo("nl")); // OK
  ResMgr.Value.GetString(Text, new CultureInfo("fr")); // OK
  ResMgr.Value.GetString(Text, new CultureInfo("en")); // returns null
  </code></pre>
  
  <p>What could possibly be the cause of this?</p>
  
  <p>Things I've tried:</p>
  
  <ul>
  <li>I've copy-pasted the key across all resource files, so I've ruled out misspelling the resource key. </li>
  <li>I've tested <code>"en-GB"</code>, <code>"en-US"</code>, <code>CultureInfo.InvariantCulture</code>.</li>
  <li>I've changed the default lanuage in the appxmanifest from <code>en-US</code> to <code>en</code>.</li>
  </ul>