Good bye....

English - Goodbye (Formal),

German - Tschüss (Informal), Guten Abend (Goodnight), Auf wiedersehen [Owf veedersehen] (informal and friendly), Bis Später (Till later)

Esperanto - Ĝis revido!

Spanish - Adiós (informal), despedida (farewell), Hasta mañana (see you tomorrow, silent 'H'), Hasta la vista (be seeing you, silent 'H'), Hasta luego (see you later, silent 'H').

In latin america: Chau (bye, informal in Argentina and Uruguay), nos vemos (see you later, informal).

Italian - ciao [chow] (informal), arrivederci (ah-ree-vay-dare-chee)

French - adieu (if this is your last time with a person) au revoir (formal, pronounced 'o-revwa') toute à l'heure, à bientot (informal, if you'll be meeting the person anytime soon)

Japanese - Ja ne, Jaa mata (only say this when you know you will be meeting the person again soon),
Sayonara (farewell)

Chinese Mandarin - Zai Jian

Chinese Cantonese - Bai bai, Joi Geen

Korean- Ahn yawng hee kah seh yoh

Arabic, Mauritanian dialect -Wa danakoum li Moulana (literally: I leave you in God's trust)

Arabic classical - Ma Assalama (formal, meaning literally: With peace) Wada an (informal) Ila liqa (only say this when you'll be meeting the person again) Assalam Alikum (meaning May peace be upon you)

Portuguese - Tchau (or Xau) (informal, pronounced like Italian ciao) Adeus (formal) Até amanhã (if you will be seeing the person tomorrow) Até Já (if you will be seeing the person soon that day) Até Logo (if you will be seeing the person later that day)

Russian: Good Bye (formal) = до cвиданиѿ (Da-sveed-DAN-ee-ya);

Tamil - Tata(informal), Sendru-Vaa(formal), Kalambu(Rude) Poyata Varayn(informal, actaully means "I will go and come")

Dutch - Formal: Tot ziens (tot seens), Informal: Doei/Doeg (oe pronounced like in 'good', g=sharp), Mazzel, Zie je later, Groetjes (greetings)

Filipino - paalam (farewell)

Hindi = dont have exactly the same word as 'Bye', but we do say something like Chalta Hu

Urdu = Khuda Hafiz (God Bless you)

Panjabi = Rub Rakha (God Bless you)

Thai = la-gon (GoodBye)