Have you done any work on trying to make the opposite? Injecting English words into Japanese text to make it easier to read? I find that students of Japanese often have enough grammar to read widely after finishing a couple of beginner textbooks, but they are completely held back by vocabulary.
I have a deep understanding of this point, a lack of vocabulary makes reading Japanese materials very difficult.
For this scenario, we will translate the Japanese text completely into English first, then inject japanese words in to the english text, the translated text with the injected Japanese words is displayed next to the original material.
This is the main feature I've been using myself, you can try it out and see if it's the feature you want.