In short: I used generative AI to program the app, but all the translations are human-made.

I'm not a software engineer and I couldn't have programmed the app all by myself. I could have hired a developer, but given how pervasive the use of AI for programming is today, I strongly suspect they would have used it anyway. At a personal level, I have complicated feelings about AI, but broadly speaking I am more anti-AI than pro-AI, at least in its current form. I have written a book that at least one AI provider illegally downloaded and used to train their model, so this is not an abstract issue, it directly affects me. At the same time, I am forced by my employer to use AI a lot in my day job, and it would feel weird to draw the line at using it myself.

With that said, if you draw the line at using any AI whatsoever, I get it, and you shouldn't use Déjà Lu. No hard feelings. I am skeptical that you'll find any new app that doesn't rely on AI one way or another, so your best bets are probably textbooks, tutors, and Anki.