  shifting them one position to the right and prepending the config.decoder_start_token_id, which for T5 is
  equal to 0 (i.e. the id of the pad token). Also note the task prefix: we prepend the input sequence with 'translate
  English to German: ' before encoding it. This will help in improving the performance, as this task prefix was used
  during T5's pre-training.
However, the example above only shows a single training example. In practice, one trains deep learning models in
  batches. This entails that we must pad/truncate examples to the same length. For encoder-decoder models, one
  typically defines a max_source_length and max_target_length, which determine the maximum length of the
  input and output sequences respectively (otherwise they are truncated). These should be carefully set depending on
