我是中国人，他是美国人，你是澳大利亚人。用英语怎么说？

第一种翻译，
I'm Chinese.
He is American.
You are Australian.
第二种翻译，
I'm a Chinese.
He is an American.
You are an Australian.
第三种翻译，
I'm from China.
He is from America.
You are from Australia.

我是中国人的英语是 I'm Chinese. 而他是美国人是 He's American. 而你是澳大利亚人则是 You're Australian. 你把这三句连起来就是应该是你想要的句子。

I am Chinese, he is American, you are Australian.
中国人Chinese
美国人American
澳大利亚人Australian; The Australian; Aussie; Australians

你好!
我是中国人，他是美国人，你是澳大利亚人。
I am Chinese, he is American, you are Australian.

I am Chinese, he's American and you're Australian.
此外还可以说：he's com from America