I think that we have two problems when we talk to foreign people. The first is learning the language. The second is learning the culture. Perhaps these are more cultural, rather than language problems? For me- it is perfectly natural to say that I need to go to bed if it is late, when I am chatting. But I do understand what you mean. For me, it was very strange when Chinese people would ask if I had eaten yet. To western people, that is an unusual question to ask. You would normally only ask that if you were going to ask someone to have a meal with you. But in China, it appears to be quite a common greeting. Similarly 'have a sweet dream' or 'sweet dreams' is quite a personal thing to say in English culture. Don't worry about it. Usually, people will be understanding, and not get offended if you say something a little unusual. Yes - 'I want to make friends with you is fine'. A little less formal would be 'Let's be friends'.