How are L-1 visa holders taxed in the United States? Are L-1 visa holders taxed on their world wide income or only income ( i.e. wages) earned in the United States?

Does the answer to above question change is the person is in the United States less than 183 days?

Also, does the answer change if the persons' country of citizenship is Australia?

I don't have an answer for your question. But, I care that your question gets answered. By my posting a reply now, your question will get moved more towards the top of the list of questions needing answers. Hopefully, someone will come along soon with the expertise to answer your question.