title: Angular2 Invalid language tag: en_US
body: <p>I would like to display a date format based on a different locale. Ideally one that I can decide upon after a query to a remote server. (The value to be put in the date field is retrieved in this same query).<br>
  I'm trying to use <a href="https://stackoverflow.com/questions/34904683/how-to-set-locale-in-datepipe-in-angular2?answertab=votes#tab-top">this answer</a> but am getting an error: <code>Invalid language tag: en_US</code></p>
  
  <p>code:</p>
  
  <pre><code>@NgModule({...
    providers: [
  {provide: LOCALE_ID, useValue: "en_US"}
  ],
  ...
  </code></pre>
  
  <p>I'm obviously missing some kind of resource, but I have no idea what.</p>