So, how do you say those things in your language? The more answers, the better! So, please, do answer for your native country
Here is answers in Finnish - my native language...
Hello= "Hei" (most common way to say hello) or "Moi" (we young people use this) or "Moikka" (also used by the youth) or "Tervehdys" (quite proper way to say hello)
Goodbye= "Moikka" (we youth use this) or "Heippa" (we youth use this) or "Näkemiin" (proper way to say it) or "Hyvästi" (you say this when you're not gonna see each other for a long time, it's quite final way to say goodbye)
Thank you= "Kiitos" (most common way to say it) or "Kiitti" (we youth use this)