Transliterate a string from the input language to English.

def _encoder(self):
    """Transliterate a string from the input language to English."""
    if self.source_lang == 'en':
      return Transliterator._dummy_coder
    else:
      weights = load_transliteration_table(self.source_lang)
      encoder_weights = weights["encoder"]
      return Transliterator._transliterate_string(encoder_weights)