class_docstr: Problem spec for English-Setswana translation.
  
  Uses the RMA Autshumato dataset.
code: def vocab_filename(self):
      return "vocab.entn.%d" % self.approx_vocab_size
  
file_path: tensor2tensor/tensor2tensor/data_generators/translate_entn.py
imports: from tensor2tensor.data_generators import problem
  from tensor2tensor.data_generators import text_encoder
  from tensor2tensor.data_generators import translate
  from tensor2tensor.utils import registry
label_desc: Use image node_id 2 for calling the TranslateEntnRma obj's underlying member method code with example usage: obj.vocab_filename() and returns: unknown