To say 'hello' and 'goodbye' to a friend who lives in Oslo, Norway, you can use the following greetings in Norwegian:
Hello: "Hei" (pronounced like "hi" in English, but with a slightly longer 'e' sound)
Goodbye: "Ha det bra" (pronounced as "hah deh brah")
In a more informal context, you can use the following casual greetings:
Hello: "Hallo" (pronounced like "hello" in English but with an 'a' sound as in "father")
Goodbye: "Adjø" (pronounced as "ah-dyuh")
Using these greetings shows your friend that you're making an effort to use their language and are being respectful of their culture. Norwegian people usually appreciate when visitors or friends try to speak a bit of their language.