Phrases and sentences; random, computer-generated or extracts of real life
There is an issue of trust, from my point of view, that is the essence of the connection between student and teacher. So that, I trust that these phrases and sentences are from "real life", and not randomly generated. And if, by necessity there needs to be random computer generated sentences and phrases, these should be marked. What say you?
here is an example of what I mean: Tu t'es récemment souvenu de sa belle voiture.
The translation of this is rather odd from my modern American point of view. Yet I don't complain, I just do my best to absorb it and repeat it, I am trusting that DuoLingo could have chosen a huge number of alternative sentences to illustrate the passe compose of etre verbs, but this was chosen for its access to French phrases heard on the street when we eventually go there. If this is just a computer generated sentence, it put in my mind a very different relationship with the material...It means that I have to put aside alot of unnecessary stuff, and just think about the grammar relationship period. Discarding distractions is an extra mental step, and I would say an unnecessary one. It is the primary responsibility for the teacher in the classroom to copy the essential and to screen out the unessential. at least at the lowest levels, which is where I am encountering this sentence.
The sentences in the Duo courses are not computer generated. Each course has a team of contributors and moderators who create the course. It might take a year... or more...before a course comes out. It takes time and patience and knowledge. The ideas, as well as the grammar, must be correct.
If you find an odd or silly sentence it's because someone had that idea. Perhaps, there was some vocabulary they wanted to include and the best idea was odd or perhaps they added a silly one to keep up interest. But all are created by humans.
Now, the correcting of the sentences is done by a computer based on the information submitted by the team. And some courses have computer-generated audio.
So, to answer your question I think it's fair to assume that of the thousands of sentences full or short the majority are from real life.