i found it hard to use language to express my fe

i found it hard to use language to express my fe

I found it hard to use language to express my feeling. 正确
I found it is hard to use language to express my feeling. 正确

两种是不同的表达，都是对的。

I found it hard to use language to express my feeling.
这里使用的是find+宾语+宾语补足语，hard 形容词做宾语it的补足语，补充说明宾语的状态、特征等。
it在这里是形式宾语，指的是use language to express my feeling。

I found it is hard to use language to express my feeling. = I found that it is hard to use language to express my feeling.
这一句是宾语从句（省略了that）。
此时it做的是宾语从句中的形式主语，指的也是use language to express my feeling。