I find Anki essential for language learning. Did it for French, starting from 0 and finishing at B2 (except for writing) in two years (also taking a 3h / week course).

Especially at the very beginning, I find learning the first 500 words as described in "Fluent Forever" very helpful. Going through that before starting with the course makes the experience much easier.

I totally agree with Krashen's theories, but using Anki is a secret weapon here that puts the process on overdrive (e.g. reading on Kindle and then later going through words that I checked in the Kindle dictionary and adding them into Anki).

Also, it's essential to retain the knowledge, e.g. if it's a language that you don't use daily.

5 years and 30'000+ cards later, I find Anki indispensable in learning anything which requires memorisation. Thinks I have to learn for work, for hobbies, certificates, improving my vocabulary in languages I care about. Basically, every fact I care about strongly enough, goes into Anki. If not enough, goes into Obsidian.

Personally, as an intermediate Japanese learner, I have been careful to choose the right input just as Krashen advocates, but I also find Anki indispensable. I found to my surprise that I have been improving about equally quickly using Anki+Animebook+Yomichan for 1-2 hours a day while living the US as I did during an earlier period when I was living in Japan (but without access to computerized methods beyond a basic pocket e-dict).

As a beginner, appropriate input was enough to care of "spaced repetition" on its own, since children's media constantly rotates over the same small set of vocabulary. But after I improved past the ~2000 most common words or so, it happened more and more that a word I recently learned didn't appear again in my input until it had already been flushed. The probability that I would actually learn a new word for good progressively decreased as I picked the lower-hanging fruit, which is the cause of the dreaded "intermediate plateau".

I gather Anki pushes out the plateau much further: I have heard that it starts to feel Sisyphean to learn new words with it around the 15000-20000 word mark instead.

Learning languages is a statistical problem.

You have to learn the high frequency words/phrases in context (forget 500 most common vocabulary lists -- those don't work). As a child, you do this naturally.

However, there are certain situations where Anki helps. I find it's with words that are useful but don't occur frequently enough to pattern match. For instance, the word "ad hoc" in English -- it occurs in professional speech, but not quite often enough for you to remember what it means in context. This is where Ankifying can really help.

Ankifying commonly confused words/phrases can also help. For instance, in English the word "put" can be used in so many contexts, and many of those contexts don't occur frequently, but can be the source of funny mistakes.

"Put up (with)" and "put out" and "put in" all mean different things in different contexts. Embedding context in your Anki cards will help you recall these contexts.

It'd be cool to have a system like chatgpt (maybe converted to audio) that you could use to practice conversations in a different language.

You have used so much jargon in your comment, that as someone who is interested in learning languages but hasn't gone into the rabbit hole for years (90% of HN?), it was tough. Perhaps says what you preach about "receive input at our level".