code: def append_fallback(model, fields):
      
      fields = set(fields)
      trans = set()
      from modeltranslation.translator import translator
      opts = translator.get_options_for_model(model)
      for key, _ in opts.fields.items():
          if key in fields:
              langs = resolution_order(get_language(), getattr(model, key).fallback_languages)
              fields = fields.union(build_localized_fieldname(key, lang) for lang in langs)
              fields.remove(key)
              trans.add(key)
      return fields, trans
docs: If translated field is encountered, add also all its fallback fields.
      Returns tuple: (set_of_new_fields_to_use, set_of_translated_field_names)