"People stay in the restaurant."
Translation:Az emberek az étteremben maradnak.
That reads more like "Some people are staying in the restaurant." Az emberek, with the definite article, is the way to make a general statement about people (which is what the given sentence seems to be).
Actually, when native English speakers construct sentences of the form "People <verb phrase>..." they mean people in general, i.e. an indefinite/undefined set of people. When they want to be specific about a definite set of people they say "The people <verb phrase>...".
- Unfortunately "People stay in the restaurant." is a pretty poor/confusing example because I do not think that most, if not all, of us native English speakers have any idea what "People stay in the restaurant." is supposed to mean. Nor is "The people stay in the restaurant." any more meaningful.
- People stay in hotels, not in restaurants. - A more useful example for learning Hungarian for English speakers example would be: "People are waiting in the restaurant" (having the connotation that some (not all) of the people in the restaurant are waiting for something, perhaps for a table, or a taxi to come pick them up, or . . .). For this example, I hope the corresponding Hungarian would be "Emberek az étteremben várnak.", or perhaps "Emberek az étteremben várva vannak".
What I can think of is along the lines of "remain", stay where they are. Or let's add this context: When it is raining outside....
But the Hungarian sentence definitely needs the "Az" here. Without it, I would need to change the word order to one of these:
"Emberek maradnak az étteremben."
"Az étteremben maradnak emberek."
"Az étteremben emberek maradnak."
And these would mean that some people stay or remain or are left in the restaurant.