That's a really interesting approach. I wonder if there are reading apps which have that dictionary integrated, but which still require a mouseover / tap to display it for a particular word (they are just using a translation language dictionary).
In my experience, a little hardship when looking up a word helps you remember it. Like having to alt-tab to a Google Translate tab vs just tapping the word inline, or having subtitles.
If it's too easy, then I found I'll look up the same words every time because it's too easy-come-easy-go.
Pleco is a high-quality dictionary app (for Chinese and only Chinese) which is currently moving into the space of selling ebooks. Dictionary features are of course integrated into the reader.
I learned Japanese to a level where I can read novels without a dictionary, more or less. I just looked the words up one by one - I think the amount of time to look up a word actually made me learn them better. If I only saw a word once, I would be less likely to look it up. If a word I didn’t know always came up, I’d look it up and write it down. You also get lots of examples of how to use a word if you look it up - a definition alone is not always the best way to learn. If you are reading online, you can use the chrome plugin rikaikun to get a mouse over lookup. But I still prefer a hard copy and an electronic dictionary.
