title: How to make ng-required working on an object value instead of the value in the input?
body: <p>I made a directive to translate in different languages using an input text. if I'm on english state and the input is empty but my model have a valid value in french. The validation only works on the value in the input text. I would like to make the attribute "required" to works if there is valid value in the part of my model that is not shown in the input. (there is no button in template, only the input and a dropdown to switch language)</p>
  
  <p>ex:</p>
  
  <pre><code>&lt;input class="form-control" type="text" ng-model="inputValue" ng-required="true"&gt;
  &lt;button ng-click="inputValue = translation.fr"&gt;Switch&lt;/button&gt;
  
  &lt;script&gt;
   var default = "en";
   function ctrl($scope) {
      var default = "en";
      $scope.translation = { fr: "Francais", en: "" }
      $scope.inputValue = $scope.translation[default]; 
   }
  &lt;/script&gt;
  </code></pre>