Greasy Fork is available in English.
Anki mode on KaniWani
You can press "space" to view the answer, "1" to mark the answer as "yes, I know this" and "2" to mark the answer as "No, I don't know this".
Instruction manual is on the WK forum thread. Link: https://community.wanikani.com/t/userscript-kaniwani-anki-mode/12557
Opinion
I like this a lot, but I don't quite understand what this adds, no documentation or explanation apart from what people already know about Anki. Please, add something for people who don't know what's being added.
Is it the X button beside the advance button in the review section? ... what does it do? thanks