docs: def get_available_voices(self, language=None, gender=None):
          """
          Returns a list of available voices, via 'ListVoices' endpoint
  
          Docs:
              http://developer.ivona.com/en/speechcloud/actions.html#ListVoices
  
          :param language: returned voices language
          :type language: str
          :param gender: returned voices gender
          :type gender: str
          """
          endpoint = 'ListVoices'
  
          data = dict()
          if language:
              data.update({'Voice': {'Language': language}})
  
          if gender:
              data.update({'Voice': {'Gender': gender}})
  
          print(data)
  
          response = self._get_response('get', endpoint, data)
  
          return response.json()['Voices']