code: def po_file_path(self):
          
          # This was formerly referred to as 'rosetta_i18n_fn'
          idx = self.kwargs['idx']
          idx = int(idx)  # idx matched url re expression; calling int() is safe
  
          third_party_apps = self.po_filter in ('all', 'third-party')
          django_apps = self.po_filter in ('all', 'django')
          project_apps = self.po_filter in ('all', 'project')
  
          po_paths = find_pos(self.language_id,
                              project_apps=project_apps,
                              django_apps=django_apps,
                              third_party_apps=third_party_apps,
                              )
          po_paths.sort(key=get_app_name)
  
          try:
              path = po_paths[idx]
          except IndexError:
              raise Http404
          return path
docs: Based on the url kwargs, infer and return the path to the .po file to
          be shown/updated.
  
          Throw a 404 if a file isn't found.