Does there exist an app/website/program that implements this technique for learning languages, combined with actual lesson plans? I understand you can use the SuperMemo software or something like Anki to learn languages, but you need to decide what you want to learn and put it into the program. What I'd like is something like Duolingo with an existing set of lessons and a progression, but that makes use of this reminder timing. (Duolingo does do reminders to practice old material, but it's clearly not advanced. It regularly has me practicing stuff that is far below my level and is effectively known forever.)
The closest thing you're probably going to find for languages is the Pimsleur method, which is also based on a specific formula of spaced repetition. I don't know how effective it would be for trying to achieve true conversational fluency, but I've found it very effective for quickly learning a basic set of words and phrases for a trip to another country.
I'm making an app like this for Japanese, however it doesn't have preset lessons yet. (I'm planning to add more structured lessons in the future.) For now what I have are a bunch of vocabulary lists for various shows/novels/etc. which you can pick and learn the vocabulary from, and then you can use the app to find the next show/novel/etc. where you'll have to learn the least amount of new vocabulary to be able to consume it.
Pre-made Anki decks vary in quality. Some are great. But none that I've found have the "themes" that personally keep me motivated to language learn long term.
