在英语中是不是不允许两个连词在一句句子里?

在英语中是允许两个连词在一句句子里的。
He would like to know if I will tell him when you come here.
if ,when 是两个连词
我是从事英语的，乐意为你解答。

应该不是吧.比如:he is taller than Jim,thought younger than Jim by far. not ...but ..till