I know this movie is fictional, but still.
Did the Nazis have time and resources to go around France "hunting" Jews?
If so, would they really search this thoroughly? I mean, they're way out in the country, where there's only the one house as far as you can see. They spend a lot of time just talking to the guy, and they're pretty polite to him too. They also are going through records of known people. Is this related to why it's illegal in France for the government to collect religious demographics today?
If the hider gave up the hiding Jews, would he really be "rewarded"? Would he actually be marked down as someone to watch closely? Would he be killed along with the Jews? What if some of the Jews then escaped like in the movie?
Is it likely that a French dairy farmer and a German soldier would really have English as their best common language? Since it's an American movie, I wouldn't be surprised if all the dialog was in English with no mention of it at all, but they begin in French.
Are the clothes and house accurate? What about the Nazi's pipe?
I cannot answer the other questions but if you are curious about the pipe, that is a Calabash Pipe, popularized in media because of Sherlock Holmes. Quentin Tarantino specifically used it for narrative purposes to portray contrast against the farmer's smaller pipe and to accentuate his detective skills.