Based on the level of respect or formality, you can say "Good luck!" in Korean in 3 ways:

• Informal: haengun-eul bilkke! (행운을 빌어!)
• Formal: haengun-eul bilkkeyo! (행운을 빌께요!)
• Very formal: haengun-eul bilgetsseumnida! (행운을 빌겠습니다!)