What does this PR do?

The input parameters of rouge/bleu are optimized. Added the ability to evaluate English data.
Rouge and bleu scores can now be evaluated more accurately, while word segmentation is automatically selected based on Chinese and English data sets.

For Chinese data

The ComputeSimilarity class in metric.py seems to be designed specifically for Chinese data sets.
In my opinion, there are two problems with the current evaluation code for Chinese data.

1. Special characters such as punctuation are not removed.
2. The current argument passed to sentence_bleu is a list of individual Chinese characters. It is better to use Chinese words in practice.

For example:

label = "你好！世界。"
reference = ['你好', '！', '世界', '。']
list(label) = ['你', '好', '！', '世', '界', '。']

• Punctuation affects the calculation of the rouge/bleu indicator
• The argument passed to sentence_bleu should preferably be ['你好', '世界']

For English data

In addition, the current code has some problems in estimating English. This is due to jieba word segmentation and other reasons.

For example, the current argument passed to sentence_bleu is a list of English letters instead of words, which does not conform to the official standard usage: nltk/translate/bleu_score

So I added code to support English data evaluation.

Fixes # (issue)

Before submitting

• Did you read the contributor guideline?
• Did you write any new necessary tests?