def METHOD_NAME(self):
    """test if reference with a valid language uses the corret templates"""
    url = reverse('index') + '?concept=data_types&lang=python%3B3'
    response = self.client.get(url)
    self.assertEqual(response.status_code, 200)
    self.assertTemplateUsed(response, 'concepts.html')
    self.assertTemplateUsed(response, 'base.html')