“他说这是两天前发生的”He says it was happened two days ago. 这样翻译对吗？

首先来纠正一下你的错误~

第一，这句话是间接引导的一句话，那么前后的时态一定要一样。
一个是SAYS，一个是WAS肯定不对嘛

第二，was happened是“被发生”的意思，什么happen啊，take place啊，这些是没有被动语态的，所以不能说was happened

那么这句话如何翻译呢？

He said it happened two days ago.
就可以了~

错.happen 是不用于被动语态的.
He said it happened 2 days before 〔ago 〕都可以

he said that it was happened two days ago!

he says this happened two days ago.