title: Angular 9 Locale data for 'en-US' cannot be found. No locale data will be included for this locale
body: <p>I am getting this strange warning </p>
  
  <p><code>Locale data for 'en-US' cannot be found.  No locale data will be included for this locale</code>
   when running <code>ng build --configuration=prod --localize</code></p>
  
  <p>here is my angular.json </p>
  
  <pre><code>// omitted
  "i18n": {
      "sourceLocale": "en-US",
      "locales": {
        "sr-Latn": {
          "translation": "src/locale/messages.sr.xlf",
          "baseHref": "/sr/"
        }
      }
    },
  // omitted
  </code></pre>
  
  <p>The documentation clearly states en-US is imported by default. 
  To make things worse, when i change sourceLocale to any other language (say 'de'), warning message goes away.<br>
  Manually registering en-US locale data doesnt help either </p>