Romance Languages:
* Spanish: Adiós (formal), Chao (informal)
* French: Au revoir (formal), Salut (informal)
* Italian: Arrivederci (formal), Ciao (informal)
* Portuguese: Adeus (formal), Tchau (informal)
* Romanian: La revedere (formal), Pa (informal)
Germanic Languages:
* German: Auf Wiedersehen (formal), Tschüss (informal)
* Dutch: Tot ziens (formal), Doei (informal)
* Swedish: Hejdå (formal), Hej då (informal)
* Danish: Farvel (formal), Hej (informal)
* Norwegian: Ha det (formal), Hei (informal)
Slavic Languages:
* Russian: До свидания (Do svidaniya) (formal), Пока (Poka) (informal)
* Polish: Do widzenia (formal), Cześć (informal)
* Czech: Na shledanou (formal), Ahoj (informal)
* Ukrainian: До побачення (Do pobachennia) (formal), Бувай (Buvai) (informal)
Other Languages:
* Japanese: さようなら (Sayōnara) (formal), またね (Mata ne) (informal)
* Chinese (Mandarin): 再见 (Zàijiàn)
* Korean: 안녕히 계세요 (Annyeonghi kyeseyo) (formal), 안녕 (Annyeong) (informal)
* Hindi: अलविदा (Alvida) (formal), ख़ुदा हाफ़िज़ (Khuda Haafiz) (informal)
* Arabic: مع السلامة (Ma'a as-salama) (formal), سلام (Salam) (informal)
Note:
* The formality level of these phrases can vary depending on the context and relationship between the speakers.
* These are just a few examples, and there are many other ways to say "bye" in different languages.
Let me know if you'd like to see more languages!