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Language learning app?
(lemmy.ca)
If it's free and open source and it's also software, it can be discussed here. Subcommunity of Technology.
This community's icon was made by Aaron Schneider, under the CC-BY-NC-SA 4.0 license.
Anki
That's the basis of Bloom's taxonomy: knowledge or memorization
Spaced repetition apps, like Anki and Duolingo help a lot with the base, the rest needs guided learning with regular activities.