Crash Nitro Kart
Key: 86 2D 34 68 3D 5D 9B 49 63 7D 40 27 D4 F8 23 C7 B0 10 A4 6F 
ELF: SLUS_206.49 

These codes will also work on the Crash Bandicoot Action Pack version of the game.

P1 Max Reverse Joker Commands
D1864082 0000????
D1864102 0000????

Skip Videos
20343258 00000000

All Cutscenes & Extra Tracks Unlocked
2079B880 DFFFBFFF

All Characters & Ghosts Unlocked (Time Trial) 
2079B884 FFFFFFFF
2079B888 FFFFFFFF

100% (Adventure Mode)
20793570 640D040C
10793574 00000101
207937E0 44239085
207937E4 50912809
207937E8 1C013804
207937EC 25008A02
207937F0 11C04280
207937F4 000004A0
207937F8 00000000
207937FC 00000000
20793800 00050000
20793804 00100020
20793808 00040008
2079380C 00000000
20793810 00000000
2079C7A4 45141500

One Lap Races
007CC0DC 00000001

1 Opponent Races
007CC0EC 00000001

2 Opponent Races
007CC0EC 00000002

3 Opponent Races
007CC0EC 00000003

4 Opponent Races
007CC0EC 00000004

Language Modifier Codes

English
00749958 00000000

French
00749958 00000001

German
00749958 00000002

Italian
00749958 00000003

Dutch
00749958 00000004

Spanish
00749958 00000005

Credit: Hacc