亡羊补牢未为迟也的英文：
[Literal Meaning]
lose/sheep/mend/barn/not/aux./late/aux.
It's not late to mend the barn even though the sheep are lost already.

[解释]
出了问题以后想办法补救，可以防止继续受损失。

[Explanation]
It's never too late to mend.

[例子]
亡羊补牢，未为迟也。你现在复习参加明年的考试也不算晚。

[Example]
It's never too late to mend. It is not too late for you to review and take the exam next year.

[英文等价词]
A stitch in time saves nine.