I'm not very familiar with Manga, but if most have a text layout similar to this image;
Then I believe we for sure could get away with just making the non-JP text slightly smaller and still keep it within the bounds of the chat bubble. I'm intrigued to solve this so you may see it solved soon (I hope!).
Yup, the layout is very often in bubbles like that. Though one thing you may want to watch out for is that the text in the green coloured boxes should be ignored since its just giving the spelling for the red colored character.
Though sometimes there is text outside the boxes, that could be fully without a box or with a strangely shaped one. (Random image examples)
I look forward to any potential implementations that could be added. :D
Thank you very much for these examples. Just so you know, I have not yet gotten around to a good solution for removing furigana. The only solution I can give you right now, if you encounter issues with that, is to make the manga zoomed out..
Also, any angled text will be troublesome, due to any text in the tool only being able to be rendered horizontally at this moment in time.
