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.
Thank you! My crux was to expand the vocabulary using texts I enjoy (not the testing itself). One could call this "very active reading", where I try to fill in words from the context.
I am developing https://vocab-boost.online/ (smoke test page, extension is being reviewed in webstore). It is a Chrome extension to make language tests out of any page. I used this approach to improve my vocabular to pass German C1 exam.