Thank you, Carlie, for asking another great question :) This is actually extremely complicated, so the best suggestion would be simply to pay attention to how your international friend introduces himself. Customs vary enormously depending on the exact relationship and context. Also, please note that with modern technology, we need to consider our choice of words from the perspective of the people we’re talking to. Even though China is the largest country in the world, there are still billions of people who live outside of China, so it’s not a good idea to lump us all together as “foreigners.” For one thing, customs are different in every country. For another, you may want to consider that the term is confusing, because a language partner in another country would actually consider you to be the foreigner. I’d recommend using a more descriptive term than “foreigner.” One idea would be the adjective “international,” in combination with a suitable noun: “international friend.” I guarantee the reaction you’ll get will be ten times more positive than if you say “foreigner.”

We very rarely address people by just their family names. In the past, people of superior rank addressed their inferiors by just their surnames. For example, if the boss was Tom Smith and his servant was John Brown, the servant would call his boss 'Mr Smith' while the boss would call his servant simply 'Brown'. Calling someone by just their surname indicates a lack of respect, and is likely to offend. Here is a general rule: Never call anyone by just their surname e.g. 'Cruise'. In a business/formal/professional context, call the person Mr Cruise or Ms Cruise. Note how they introduce themselves - if the person says 'Hi, I'm Tom', you can call them Tom. If they don't, you should be polite and call them 'Mr Cruise'. They may then tell you to call them Tom. In an informal contexts and among young people, for example, with fellow students, use their first name ('Tom' or whatever their given name is).

You can call your friends' first name. Even when you met first. Or you can ask , it'd be conversation starter. And it changes country to country. Of course in formal situations you should call him/her with his family name mostly. For example in Turkey, you should call with first names. Your friends, maybe friends' parents. Even to a doctor we say ' first name' bey/hanım ( it is like Mr/mrs/miss )