I just found out about Lute, a platform that allows for reading content while providing translation and tracking of words. It seems to be based on LWT (Learning with Texts), which is, itself, inspired by (according to the Abstract section in their website),

- Stephen Krashen's principles in Second Language Acquisition,

- Steve Kaufmann's LingQ System and

- ideas from Khatzumoto, published at "AJATT - All Japanese All The Time".

I bookmarked Krashen to read later (it has lots of content and writings on the subject); as for LingQ, I had already heard of it in passing, but did not get too interested — it is clearly a paid service. I tried it today, briefly — and it seems good (even if, for the sake of principle, I will not use it): one could listen/watch Youtube videos with word-by-word highlighting, while providing on-demand translation and, again, tracking of individual words. I did not follow up on any of Kaufmann's thoughts about language learning.

At the moment I am currently pursuing the development of my own tooling to advance my learning; but the space is clearly already well-populated, even though, as usual, open-source solutions are still a bit behind.

By chance, also found the Language Learners platform, which seems to be related to the How To Learn Any Language website.

Other resources to check out: Alexander Arguelles seems to have some interesting things, and Iversen's guide to learning languages; Ever Onward! How to Improve Your Advanced Language Skills