No repeated directors. No repeated decades. No repeated genres. No repeated countries.
All still classics.
Sound difficult? It is. Here are two examples of how it can be done.
00s City of God - Brazilian Thriller: Meirelles and Lund
90s Chungking Express - Chinese Romance: Kar-Wai
80s Cinema Paradiso - Italian Drama: Tornatore
70s Solaris - Soviet Sci-Fi: Tarkovsky
60s Yojimbo - Japanese Action: Kurosawa
50s Smiles of a Summer Night - Swedish Comedy: Bergman
40s Fantasia - American Animation: Disney
30s Olympia - German Documentary: Riefenstahl
20s The Passion of Joan of Arc - French Biopic: Dreyer
00s Paprika - Japanese Animation: Kon
90s Farewell My Concubine - Chinese Epic: Kaige
80s Wings of Desire - German Romance: Wenders
70s The Discreet Charm of the Bourgeoisie - French Comedy: Bunuel
60s 8 1/2 - Italian Drama: Fellini
50s The Apu Trilogy - Indian Biopic: Ray
40s The Third Man - British Thriller: Reed
30s The Wizard of Oz - American Musical: Fleming
20s Man With a Movie Camera - Soviet Documentary: Vertov