code: def convert_to_duckling_language_id(cls, lang):
          
  
          if lang is not None and cls.is_supported(lang):
              return lang
          elif lang is not None and cls.is_supported(lang + "$core"):   # Support ISO 639-1 Language Codes (e.g. "en")
              return lang + "$core"
          else:
              raise ValueError("Unsupported language '{}'. Supported languages: {}".format(
                  lang, ", ".join(cls.SUPPORTED_LANGUAGES)))
docs: Ensure a language identifier has the correct duckling format and is supported.