This bundle uses Google to translate messages that you have not translated yet. So instead of using a fallback language you get a Google translated string. Sure, Google translate is not optimal but it is way better then using a different language. With this feature you can deploy a new version even before your translators have done their work.

Run the following in your project root, assuming you have composer set up for your project

composer require happyr/auto-fallback-translation-bundle

Add the bundle to app/AppKernel.php

class AppKernel extends Kernel
{
  public function registerBundles()
  {
    $bundles = array(
        // ...
        new Happyr\AutoFallbackTranslationBundle\HappyrAutoFallbackTranslationBundle(),
    }
  }
}

// app/config/config.yml
happyr_auto_fallback_translation:
    enabled: false
    default_locale: en
    translation_service: "google"
    google_key: "%google_server_api_key%"
    http_client: httplug.client.auto_translation
    message_factory: httplug.message_factory # default
    
 // app/config/config_prod.yml
happyr_auto_fallback_translation:
    enabled: true # Only enabled in production

To easier configure the HTTP client and message factory, have a look at HttplugBundle.