没有任何权威性，仅供参考的答案：

英译汉:

Here's my advice to you: don't marry until you can tell yourself that you've done all you could, and until you've stopped loving the women you've chosen, until you see her clearly, otherwise you'll be cruelly and irremediably mistaken. Marry when you're old and good for nothing...  Otherwise all that's good and lofty in you will be lost.  

― Leo Tolstoy

我给你的忠告是： 千万别 (和她）结婚，除非你确信自己已无可追求，除非你对所有你曾属意的女人都不再有爱，除非她对你不再有神秘感。否则你就是做了严重的无可弥补的误判。 不到你老朽无用的时候不要结婚...  否则你本身所具有的所有亮点都将泯灭无遗。

汉译英:

第三次世界大战用什么武器我不知道，但是第四次世界大战肯定是用棍子和石块打的。

I know not with what weapons World War III will be fought, but World War IV will be fought with sticks and stones.

Idiom: （can't) wrap sb's head around something

弄懂/弄不懂