before_sent:  The approach - tag-less back-translation - trains the model on the synthetic data and finetunes it on the natural data.
before_sent_with_intent: <fluency>  The approach - tag-less back-translation - trains the model on the synthetic data and finetunes it on the natural data.
after_sent:  The approach - tag-less back-translation - trains the model on the synthetic data and fine-tunes it on the natural data.