Because there is no verb involved in "Goodbye," you can simply say "Adiós" just as you would with any other person. If you are really looking to be super formal, you can say "Me despido de usted," but it's not something that is commonly said in the Spanish language.
"Do widzenia!" Translated word for word it means "Until I see you again!" and that's a phrase you can say to anyone, formally, or informally. However, if you just want to say bye to a friend or someone close you can just say "Cześć!". This is a word which can be said as Hello OR Goodbye.
Ya Ssou is "Hello or Goodbye", in Greek to one person or a friend. * "Athio" [αντίο] or (formally) "Athio sas" is goodbye in Greek. Yia sou is usually used for hello, however it is also used as goodbye by some people.
In Cebuano, you can say "paalam" to say goodbye.
In Zuni, you can say "yawakwi" to say goodbye.
In Ibanag, you can say "Agyamanak!" to say goodbye.
I Will Say Goodbye was created in 1980.
In Swati, you can say "sala kahle" to say goodbye.
In Dene, you can say "Mahsi cho" to say goodbye.
In Kpelle, you can say "Ka boss" to say goodbye.
goodbye
Goodbye