At the 'Main' menu hold L + R and press Down, X, Up, Y, Down, Down, Up, Up. A 'Cheat' option will appear when you release L + R, select it and enter the following case-sensitive codes.

God Mode --> 8wonde
Bonuses Completed --> KKmuseum
One-Hit Kills --> GrosBras
999 Ammunition --> KK 999 mun
Machine gun --> KKcapone
Revolver --> KKtigun
Shotgun --> KKsh0tgun (contains number '0')
Level Select --> KKst0ry (contains number '0')
Unlimited Spears --> lance 1nf (contains number '1')
Sniper Rifle --> KKsn1per (contains the number '1')