There is a learning method called Spaced Repetition, which involves repeatedly quizzing yourself, with a decreasing frequency as you learn them. So, if you always know the word for dog, you'll get that one less frequently than the one for cat that you have more trouble remembering.

I use Anki with Yomichan to study Japanese and find it very effective.

I built an iOS app for studying Japanese called Manabi Reader. It collects interesting short-form reading materials, has one-tap dictionary lookups, and lets you add words to flashcards.

I'm currently working on extending it with word tracking functionality, so that you can see which words in an article are new to you, can track your progress through kanji by reading, etc.

https://reader.manabi.io

How do you solve the problem that almost all interesting material is copyrighted? I use texts from https://www.aozora.gr.jp/ but most of those are somewhat old-fashioned, except for a few modern Japanese translations of foreign public-domain literature.

The app is a dressed-up RSS reader

This app does this exceptionally. It does limit you to 5 minutes a day though, but at times does offer you more time. https://languagedrops.com/

This makes sense. The act of recalling it is what cements your 'knowledge' of it, and repeating that recollection makes it easier to draw that connection each time.

It's not really how we learn new things. We see, hear, experience them in context many times, not force ourselves to recall them. Forced repetition is one of the worst most inefficient approaches to language learning.

I've found spaced repetition a great way to increase the size of my vocabulary whilst learning a language. You're right that it's unnatural, but a large unnaturally-learned vocabulary can then be polished by practice in more natural contents, and I feel like the net result is more efficient than using the natural contexts alone. This is especially true since I do not have easy access to native speakers for half an hour every day, but I can practice with the Anki app whilst on public transport during that time.

Last time I learned a language (German), a small vocabulary was my perpetual weakness. Now I'm learning a different language (Spanish) with a different approach that makes heavy use of spaced repetition, and vocabulary is no longer my weakest point. Instead, listening comprehension is now my weakness. But with a decent vocabulary, I am now working on improving the listening comprehension using podcasts. If my vocabulary were weaker, this would be much more difficult as I would need access to a native speaker who would considerately restrict themselves to mostly use vocabulary I know.

One thing that’s helped a lot with my listening comprehension is following along in a printed book with an audiobook reader. Especially when it’s a translation of a story I already know, I can usually more or less follow the plot and let the language information seep into my unconscious.

Thanks for the tip! That's one thing that hadn't occurred to me to try. I've tried the same thing with TV/movies, but the subtitles are usually not identical to the spoken dialog - they tend to be simplified and paraphrased to be shorter - but eBooks should be very faithful to their written counterparts.

From my experience, spaced repetition is only really useful as a trigger to recall prior meaningful experiences. The really tricky part of using spaced repetition well is writing the cards: you need to work with new material until it feels obvious, and only then make cards that will recall that experience of it being obvious.

For language learning, there’s one other wrinkle: you need to be working with material written in the target language, rather than written about the target language. Most of my language cards are Cloze deletions from novels I’ve read or museum captions, for instance.

The idea that scheduling recall repeatedly is a poor and inefficient approach to learning is directly contradicted by all available research on learning and memory.

See [0] for a review of the research on spaced repetition.

[0] https://www.gwern.net/Spaced-repetition

My feeling on learning a language is that you break down a language barrier to find an even more difficult cultural barrier.

That's what I always told my friends when I was an expat. You can learn your girlfriend's language, but you'll never get her jokes. :)

it's not just repetition, it's use in context. I learned both spanish and english that way, and I did it extremely quickly. Whenever you encounter a new word, work it in a sentence, then use it with someone else in a real situation. I guarantee your gains are going to be measurable day by day.