code: def validate_language_key(obj, key):
      
      backend = bigchaindb.config['database']['backend']
  
      if backend == 'localmongodb':
          data = obj.get(key, {})
          if isinstance(data, dict):
              validate_all_values_for_key_in_obj(data, 'language', validate_language)
          elif isinstance(data, list):
              validate_all_values_for_key_in_list(data, 'language', validate_language)
docs: Validate all nested "language" key in `obj`.
  
         Args:
             obj (dict): dictionary whose "language" key is to be validated.
  
         Returns:
             None: validation successful
  
          Raises:
              ValidationError: will raise exception in case language is not valid.