Probably only works for dumb bots and I’m guessing the big ones are resilient to this sort of thing.
Judging from recent stories the big threat is bots scraping for AIs and I wonder if there is a way to poison content so any AI ingesting it becomes dumber. e.g. text which is nonsensical or filled with counter information, trap phrases that reveal any AIs that ingested it, garbage pictures that purport to show something they don’t etc.
What I’d wonder is why it’s such massive expensive for Duolingo to hire 2 or 3 people to cover a language anyway. Presumably most of the work is contractual - hire somebody competent to produce a course, get somebody to say the lines, refine the course based on feed back and that’s mostly it.