期待你的回信英文是 "Looking forward to your reply"。这个短语的来源是在英语中经常用来表达等待某人的回信或回复的意思。例句如下：

I'm looking forward to your reply to discuss further details.

We look forward to your reply and would appreciate if you could let us know your availability for the meeting.

Thank you for your email. We look forward to your reply.