Convert a sequence of bpe words into sentence.

def _bpe_to_words(sentence, delimiter='@@'):
    """Convert a sequence of bpe words into sentence."""
    words = []
    word = ''
    delimiter_len = len(delimiter)
    for subwords in sentence:
        if len(subwords) >= delimiter_len and subwords[-delimiter_len:] == delimiter:
            word += subwords[:-delimiter_len]
        else:
            word += subwords
            words.append(word)
            word = ''
    return words