https://qiita.com/kenrohmiyoshi/items/8d767242da8ec87b8962
https://www.crosslanguage.co.jp/blog/nmt-smt-rbmt/
http://deeplearning.hatenablog.com/entry/unsupervised_machine_translation
https://gigazine.net/news/20181012-language-translator-deep-learning/
https://www.bcm.co.jp/solution-now/cat-solution-now/cat-now-ai/2018-08_1109/