angular.module('myApp', ['pascalprecht.translate']);

angular.module('myApp')
  .config(['$translateProvider',
    function($translateProvider) {
      $translateProvider.registerAvailableLanguageKeys(['de_DE', 'en_US'], {
        'en_US': 'en_US',
        'en_UK': 'en_US',
        'en': 'en_US',
        'de': 'de_DE'
      });

      $translateProvider.useStaticFilesLoader({
        files: [{
          prefix: 'lang_',
          suffix: '.json'
        }, {
          prefix: 'foo/lang_',
          suffix: '.json'
        }]
      });

      $translateProvider.use('de_DE');
      $translateProvider.fallbackLanguage("en_US");
    }
  ]);

angular.module('myApp').controller('someController', ['$scope', '$translate',
  function($scope, $translate) {

    $scope.switchLanguage = function(key) {
      $translate.use(key);
    };
  }
]);
<!doctype html>
<html ng-app="myApp">

<head>
  <meta charset="utf-8">
  <title>AngularJS Plunker</title>
  <script>
    document.write('<base href="' + document.location + '" />');
  </script>
  <link rel="stylesheet" href="style.css">
  <script src="https://cdnjs.cloudflare.com/ajax/libs/angular.js/1.7.5/angular.min.js"></script>
  <script src="https://cdnjs.cloudflare.com/ajax/libs/angular-translate/2.18.1/angular-translate.min.js"></script>
  <script src="https://cdnjs.cloudflare.com/ajax/libs/angular-translate/2.18.1/angular-translate-loader-static-files/angular-translate-loader-static-files.min.js"></script>
  <script src="app.js"></script>
</head>

<body ng-controller="someController">
  <h1 translate>HEADLINE</h1>
  <!-- <h2 translate>YOU</h2> -->
  <button ng-click="switchLanguage('de_DE')" translate="LANG_DE_DE"></button>
  <button ng-click="switchLanguage('en_US')" translate="LANG_EN_US"></button>
</body>

</html>
/* Put your css in here */


{
 "HEADLINE": "Hello da!",
 "LANG_DE_DE": "Sprache: Deutsch",
 "LANG_EN_US": "Sprache: Englisch"
}
{
 "HEADLINE": "Hello there!",
 "LANG_DE_DE": "Lang: German",
 "LANG_EN_US": "Lang: English"
}
{
 "YOU": "How are you?"
}
{
 "YOU": "Wie geht es dir?"
}