code: def handle(self, source, target, app=None, **options):
          
          translation.activate(settings.LANGUAGE_CODE)
          if app:
              unpack = app.split('.')
  
              if len(unpack) == 2:
                  models = [get_model(unpack[0], unpack[1])]
              elif len(unpack) == 1:
                  models = get_models(get_app(unpack[0]))
          else:
              models = get_models()
              
          for model in models:
              if hasattr(model, 'localized_fields'):
  
                  model_full_name = '%s.%s' % (model._meta.app_label, model._meta.module_name)
                  update_instances = set()
                  messages = []
                  
                  for instance in model.objects.all():
                      for field in model.localized_fields:
                          source_field = get_real_fieldname(field, source)
                          target_field = get_real_fieldname(field, target)
                          
                          if  hasattr(instance, source_field) and hasattr(instance, target_field):
                              source_field_value = getattr(instance, source_field)
                              target_field_value = getattr(instance, target_field)
  
                              if target_field_value in (None, u'')\
                                  and source_field_value not in (None, u''):
                                  setattr(instance, target_field, force_unicode(source_field_value))
                                  update_instances.add(instance)
                                  messages.append(u"%s %s %s will become %s" % (model_full_name, instance, target_field, force_unicode(source_field_value)))
  
                  if len(update_instances):
                      if self.ask_for_confirmation(messages, u'%s.%s' % (model._meta.app_label, model._meta.module_name)):
                          for update_instance in update_instances:
                              print u"saving %s" % update_instance
                              update_instance.save()
docs: command execution