如果你想对你的朋友说明他/她的英语不好，你可以这样说：
"Your Engpsh isn't very strong."
或者：
"Your Engpsh needs some improvement."
当然，你也可以用更加礼貌的语言来表达：
"I think you would benefit from some additional Engpsh practice."
或者：
"I noticed that your Engpsh pronunciation could use some work. Do you want to practice together?"
重要的是，你应该确保你的评论是友好的，而不是贬低性的，并且应该在表达你的看法时尽量保持尊重。