Enabling MT_SERVICE results in Internal Server error

Question

Regardless of which MT_SERVICES I try to enable in settings.py, after restating Apache, I get an Internal Server error when accessing the site. I tried to enable one or two services, but did always get the same problem.

I tried enabling different services. Nothing worked. When I remove the MT_SERVICES, everything is back to normal.

MT_SERVICES = (
    'weblate.machinery.deepl.DeepLTranslation',
    'weblate.machinery.saptranslationhub.SAPTranslationHub',
)
MT_DEEPL_KEY = xxxxxx

MT_SAP_BASE_URL = xxxxxx
MT_SAP_SANDBOX_APIKEY
MT_SAP_USERNAME = xxxxxx
MT_SAP_PASSWORD = xxxxxx
MT_SAP_USE_MT = True

Result: Error: Internal Server Error