The old phrase was " when pigs fly."

古语是“猪飞时” 。

" When pigs fly" is meant to indicate an impossible condition.

“When pigs fly” 是指不可能的情况。

Could be tomorrow, could be when pigs fly.

也许是明天 也许要等猪飞上天了。

The last phrase involving pigs is: When pigs fly.

最后一句涉及猪的是：When pigs fly。

And this essentially means that something will happen when pigs fly.

这实质上意味着当猪飞起来时会发生一些事情。

Now we all know pigs can't fly, so when we say " When pigs fly" .

现在我们都知道猪不会飞，所以当我们说“When pigs fly”。