Readlang is already very effective 
for learning Japanese thanks, among other things, to the Explain feature and the non-distracting UI. But the experience could improve significantly 
through implementation of the following improvements. (Some of them seem as if they should be rather easy to implement).
- Most pressing would be to have Readlang persist
in displaying saved/highlighted words within texts. Currently, it doesn’t auto-highlight saved words upon page refresh. Naturally, saved words don’t auto-highlight from one text to another either. - Next would be to have Readlang display alternate readings
. I don’t have examples on me, but Readlang only looks to display a single Kanji reading. This means Kanji readings will be completely incorrect within certain contexts, from which they may be saved. They then display the wrong readings in practice mode too. (Of course, dictionaries and the Explain feature get readings correct). - Finally would be to have Readlang parse
Japanese words correctly. I saw the reasons why this currently isn’t supported in: (How does word splitting work in Japanese?). Nevertheless, without good parsing, I think it is very difficult for newer Japanese learners on Readlang to be comfortable reading; on the other hand, this is a relatively insignificant issue for users already somewhat familiar with basic Japanese sentence structure.
By implementing these improvements, Readlang will be much more attractive 
to the vast community of Japanese learners on the internet. With the above issues present, I’m sure many are scared away 
because it looks as if Readlang hardly supports Japanese, when opening a text for the first time.