These are ones I like, not necessarily important, although some are indeed essencial. Literature only.
Portuguese - you can’t go wrong with Fernando Pessoa (anything), Graciliano Ramos (Angústia), Machado de Assis (Dom Casmurro), Saramago (Lições de pintura e caligrafia), Moacyr Scliar (Exército de um homem só), Inácio de Loyola Brandão (Não verás país nenhum), Lya Luft (A asa esquerda do anjo), Raduan Nassar (Um copo de cólera).
French - Madame Bovary, Eugenie Grandet, Le Père Goriot, L’Étranger, Candide, Le rouge et le noire, Notre-Dame de Paris, Le Comte de Monte Cristo, À la recherche du temps perdu and so many others.
Russian - Crime and Punishment, Brothers Karamazov, Notes from the Underground, War and Peace, Anna Karenina, The Master and Margarita, We, Heart of a Dog, Fathers and Sons, Dead Souls.
German - The Metamorphose, The Magic Mountain, Demian, Faust, Werther, Kassandra, Buddenbrooks, Death in Venice, Siddhartha, The Glass Bead Game.
English - Ulysses, Portrait of the Artist as a Young Man, Winesburg Ohio, Waiting for Godot, The Playboy of the Western World, 1984, Brave New World, Ubik, Hamlet, Macbeth, King Lear, Dr. Faustus, Volpone, The Sound and the Fury, Moby Dick, LIght in August, Watership Down, Farenheit 451, Martian Chronicles, Something Wicked This Way Comes, Mrs. Dalloway, Wide Sargasso Sea.
I’m going to stop short of delving into my Sci Fi and Fantasy obsession too much.