@registry.register_problem
class TranslateVndt(translate.TranslateProblem):
    @property
    def approx_vocab_size(self):
        return 2**15  # 32768

    def source_data_files(self, dataset_split):
        train = dataset_split == problem.DatasetSplit.TRAIN
        return _VNDT_TRAIN_DATASETS if train else _VNDT_DEV_DATASETS

@registry.register_hparams
def transformer_base_h256():
    hparams = transformer_base()
    hparams.hidden_size = 256
    return hparams