While I’ve been using LingQ for French for a few years, a few months ago started using it daily too to refresh my old B1ish level understanding of Japanese. Back in the day, I could read about 1,000 kanji.
I still kinda have this question myself about how to use LingQ effectively with Japanese.
First, I’d say that LingQ isn’t really designed to help learn kanji. If it was, it would help track kanji known as robustly as it tracked words known. For instance, what if LingQ visualized words known, as it does, with the background colorization, but also employed colorized underlining of unknown and partially known individual kanji at the character level? What if LingQ provided the user the ability to click on individual kanji to then see the kanji’s on and kun yomi, the meanings, the stroke count, the radical used for dictionary ordering, the composite radicals more loosely definied, an animation with stroke order, etc. [even as other software has done for 20 years]? The LingQ design team simply hasn’t prioritized such as this. With Steve’s personal language background, this kind of surprises me.
All this being said, I suspect the best practice is to mark the word known when all its kanji are known, with at least the meaning and on/kun yomis as used in the given word.
Then the next question is, do you identify it as known when you can only read it? Or when you can write it? Generally, in other languages, LingQ works best when you mark it as “known” when the word is in your active vocabulary. In an alphabet-based language, there’s little distance between being in active spoken vocabulary and an ability to write. With Japanese, it’s particularly large between the number of on and kun pronunciations an individual kanji can have. So here, to use LingQ effectively, I think the question has to be, what your goal? Is it to be able to a) speak and read?, b) write with the aid of modern online tools, or c) write old fashioned pen [or brush!] and paper?
Personally, when I studied Japanese first many years ago, I put soooo much time into writing by hand. I regret the amount of language study time I put into that skill. I wish I had just focused on being able to speak and read. As such, now in re-learning/re-freshing Japanese, I mark a word know when I can read it with the correct pronunciation without the aid of furigana, romaji or similar. When you mark it known may depend upon what your language learning goals are.
Now, that said, this gets me to another LingQ problem. This one isn’t a feature limitation but more simply bugginess in my opinion. Sometimes, the LingQ software gets the on and kun readings wrong. Others can correct me if I’m wrong, but I believe this issue and its relationship with breaking sentences up into words has been brought up to the LingQ support team with rather unurgent “we’ll look into that” responses.
All that being said, I’ve been using LingQ as a fairly effective tool to help refresh in my brain the Japanese I learned years ago. I just have to check on and kun readings sometimes when I don’t trust LingQ.