I've been developing a Chrome extension for learning foreign language vocabulary from sites you love - http://vocabboost.online/. Basically, it makes fill-in-the-blanks quiz out of any webpage. It is language agnostic (just relies on word separators), so it works with almost all languages. Users asked to support Japanese, so I use TinySegmenter for Japanese word separation. Recently I added a word bank feature to save interesting words and export them.