gistfile1.js

// My region controller, it's located where the application it's booted
App.mainRegion.on("show", function( view ){
  window.onViewRendered( view );
});



// The function which it's been called - The rendered view was passed by the regionManager
window.onViewRendered = function (renderedView){

  languageFiles = ['system', 'appBar', 'etc...'];
  
  // I've created a local var which it's responsible for defer the onShow method, 
  var onshow = renderedView.onShow
  
  // So, even if the Marionette layout manager dispatch the child itemView on show event, it will be undefined
  renderedView.onShow = undefined;
  
  // At this function, i load some json files, and the Marionette control was executing child itemView on show before this function really finish
  // Your example about using $.then would be used here, but with the workaround of turning onShow undefined solves the problem
  translateContent(languageFiles, {}, function(){

    // Apply some default things on the view

    // Here's the workarround... I finally call the onShow, passing the view reference
    onShow.apply(renderedView);
  });
}


// Loads the json files, so it takes a bit to response the callback
window.translateContent = function(namespaces, data, callback) {
  console.log('helper.js --------> translateContent');
  if(_.isEmpty(namespaces)) namespaces = 'dashboard';
  if(typeof data != "object") { data = {}; }


  if($.i18n.exists(namespaces+':'))
  {
    App.mainRegion.$el.i18n(data);
    if(typeof callback == "function") { callback(); }
  }
  else
  {
    $.i18n.loadNamespaces(namespaces, function() {
      App.mainRegion.$el.i18n(data);
      if(typeof callback == "function") { callback(); }
    });
  }
}