You know you need a break when you forget which language you're typing in. I was thinking about how to spell Wiedersehen (I got it right) and somehow ended up typing "Thanks, auf Wiedersehen" instead of "Danke, auf Wiedersehen." Oops!
I am learning Spanish in Duo, Mango, and school. Once, before switching to German, I tried Norwegian in Mango. I would say the words out loud, but kept mixing up my Spanish with the Norwegian! :P Even happens on German here sometimes. XD
Generally auf means on. Literally "wieder" means again and "sehen" means to see. So auf wiedersehen is like, until we see eachother again. Although it is a bit formal, most people would just say "tschüss", meaning bye.