I asked quite a few waiters,who said nothing but smiled at m

I asked quite a few waiters,who said nothing but smiled at me,before the message registered that my English was not good enough.
前面我看得懂但是从before后就不懂了（词义我都知道）
我想问1：before是介词后能跟句子吗?
2：the massage和 registed之间是不是有什么从句什么的别省略了?
3：before the message registered that my English was not good enough.到底是什么结构啊,