Enable automatic translation export in the test environment

Fixes #2016

config/environments/test.rb

@@ -41,6 +41,9 @@ Rails.application.configure do
   # Print deprecation notices to the stderr.
   config.active_support.deprecation = :stderr
 
+  # Export translations automatically
+  config.middleware.use I18n::JS::Middleware
+
   # Raises error for missing translations
   config.action_view.raise_on_missing_translations = true
 end