code: def get_lang(tweet):
      
      if is_original_format(tweet):
          lang_field = "lang"
      else:
          lang_field = "twitter_lang"
      if tweet[lang_field] is not None and tweet[lang_field] != "und":
              return tweet[lang_field]
      else:
          return None
docs: Get the language that the Tweet is written in.
  
      Args:
          tweet (Tweet or dict): A Tweet object or dictionary
  
      Returns:
          str: 2-letter BCP 47 language code (or None if undefined)
  
      Example:
          >>> from tweet_parser.getter_methods.tweet_text import get_lang
          >>> original = {"created_at": "Wed May 24 20:17:19 +0000 2017",
          ...             "lang": "en"}
          >>> get_lang(original)
          'en'
  
          >>> activity = {"postedTime": "2017-05-24T20:17:19.000Z",
          ...             "twitter_lang": "en"}
          >>> get_lang(activity)
          'en'