I watched this because after watching the trailer, I saw this was a remake of Sacha Guitry's La poison (1951) - which is one of the best movies I've seen.
Jojo (Jacques Villeret) is a hard-working farmer in Le paradis (the name of the farm), which belongs to his wife Lulu (Josiane Balasko). They can't stand each other. The movie begins with Lulu makes holes on the bottom of Jojo's milk buckets, so that his goats' milk are wasted. She cooks food he doesn't like and put lots of salt in his soup. He cannot divorces her because that means he will sleep on the street. After Lulu burned his stamp collection, Jojo is at his wit's end. He happens to see on TV a brilliant lawyer who always succeeds in acquitting his clients. Jojo goes to see this lawyer and tells him that he has killed his wife. The lawyer supplies him with the details and Jojo goes home, accidentally kills his wife, who has put mole poison in his drink, exactly in the way described by the lawyer. The prosecutor who comes to the murder scene is given the poisonous drink, but his life is safe. [If I am not mistaken, in La poison, the poison is drunk by the pharmacist and he dies.]
The lawyer has to take Jojo's case, of course. The trial is funny, with a very long philatelic discussion between Jojo and the judge, who happens to be an avid stamp collector, too. There is also a question from the 7th juror (from George Lautner's Le septième juré). Jojo spends less than 2 years in prison and goes home to his dear farm, which has been taken care of the villagers while he is in prison.
I like La poison much better than this Un crime au paradis. In La poison, I like very much the scene where the children play 'husband and wife'. The case is so popular that the villagers' children pretend to kill each other when they play husband and wife. Horrible, but hilarious.