" 英语科代表“用英语怎么说？

科目＋monitor
e.g. 英语课代表english monitor

In general, 代表 would be translated as representative. But in your case, this title may imply something different since the person may be the best in the subject, and hence may be translated as a "delegate".

也就是说,英语科代表的说法应该是
english delegate

English representative of the class
一般简化为English Rep.

English representative of the class

representative of English class