I loved Memrise for custom vocab decks, but they got rid of that feature in favour of focusing on their own language causes. I did their intro to Japanese about 10 years ago and I wouldn’t recommend it if you were seriously considering learning a language. I don’t know how it is now, but they didn’t really explain grammar, so you were left working it out based on the sentences it got you to memorise. If you actually want to learn a language through self-study, a textbook is the best way to go. And use Anki for vocab learning.