class_docstr: Problem spec for WMT En-Zh translation.
  
  Attempts to use full training dataset, which needs website
  registration and downloaded manually from official sources:
  
  CWMT:
    - http://nlp.nju.edu.cn/cwmt-wmt/
    - Website contains instructions for FTP server access.
    - You'll need to download CASIA, CASICT, DATUM2015, DATUM2017,
        NEU datasets
  
  UN Parallel Corpus:
    - https://conferences.unite.un.org/UNCorpus
    - You'll need to register your to download the dataset.
  
  NOTE: place into tmp directory e.g. /tmp/t2t_datagen/dataset.tgz
code: def approx_vocab_size(self):
      return 2**15
  
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  import os
  from tensor2tensor.data_generators import generator_utils
  from tensor2tensor.data_generators import problem
  from tensor2tensor.data_generators import text_encoder
  from tensor2tensor.data_generators import text_problems
  from tensor2tensor.data_generators import translate
  from tensor2tensor.utils import registry
  import tensorflow.compat.v1
label_desc: Use image node_id 1 for calling the TranslateEnzhWmt32k obj's underlying member method code with example usage: obj.approx_vocab_size() and returns: unknown