嗯,你的疑问我理解,是这样的：
I found that to learn English is important . = I found it important to learn English .. 一句中涉及到的语法点主要有形式宾语和宾语补足语问题,I found it important to learn English .在这句中由it充当形式宾语,而真正的宾语是to learn english.所以important在这充当宾语补足语,它的逻辑主语就是to learn English了!（现在我们用I found it important to learn English .表达多一点!
希望能帮到你,望采纳!