Sorry to get in on your reply to another poster, but it depends who the lecture is given to. Students, who are to go abroad for further studies, ought not to be treated with bilingual presentations unless a cultural point is to be made. Such students must be able to comprehend explanations or synonyms in English and professors ought to be trained to do so. I'd go as far as to say that any uni students of English as the second language at independent level of English should not be aided their first language too. Even if they learn English for some purpose in their homeland, they should develop that "switch" from Chinese to English or the other way around when necessary. Otherwise, they'll never be able to use English properly and they'll be affected in a few different ways when dealing with English in future.