When translating 잘자요 and 굿나잇 they both come up as meaning "Good night".
Is there a contextual difference between them, if so what is this difference and when do I have to use which one?
With my family, we typically use "잘자요" or some variation of it when we are speaking to each other before going to sleep. However, sometimes, if we are using Kakaotalk (Korean SNS/Messenger application) we may say "굿나잇" - it tends to give off a kind of cute vibe (in my personal opinion).
Source: Native English speaker, married to Korean