He speaks English as well as,if not betterthan,our english teacher .

与He speaks English as well as our English teacher,if not better than him.相同

他说英语即使不必我们英语老师说的好，也和他差不多。

两个句子意思相同。

插入语放句子中间~

如果不是比他更好，他说英语和我们的英语老师一样好 再看看别人怎么说的。

如果不是更好的话，他的英语说得（至少）和我们英语老师一样好。

他的英语水平即使不比老师好，也是和老师一样好。

He speaks English as well as,if not better than,our english teacher. if not better than为插入语，起补充作用，后面接than的对象our English teacher. 也就是补充“He speaks English as well as our English teacher.”这句话的意思。 那么就和下面这句话是一样的了， He speaks English as well as our English teacher,if not better than him. 只是if not better than放在了句末，于是than后面的对象就用了him来代替our English teacher 所以两句话的意思是一样的。 有问题可以继续问我。