You should reply to let the person who sent the invitation know whether or not you plan to go.

你应该回复，让发出邀请的人知道你是否打算去。

youdao

Reply like you would to any invitation.

像答复任何邀请一样答复它。

youdao

For example, if you send me an invitation to speak at a conference and I ask what the topic is, you might reply with just the topic, snipping out all the details of the conference.

举个例子，如果你给我发送一封邮件，邀请我在一个会议上发言，我问发言的主题是什么，你可能只回复我这个主题，剪去了所有关于这个会议的细节。

youdao

The Iranian government also did not reply to an Italian invitation to participate in talks on the sidelines of the G-8 foreign ministers meeting later this week in Trieste.

VOA: standard.2009.06.24