很难理解英文

It's too hard to understand.或者It's very hard to understand.或者It's so hard to understand.

It is so difficult to understand/comprehend/figure out.

That's too difficult to understand.

你句中的 except 写错了,应为expect. 下面是原句出处: Your letter made me happy. I did not expect such a full return. 你的来信使我很高兴, 也非常出乎意料.

难以理解Difficult to understand

It's hard to understand.