“请君入瓮”就是“以其人之道还治其人之身”的意思。有的汉英字典把“请君入瓮”翻译成"Please get into the jar, sir!" 这样翻译只是把字面意思翻译出来，但是成语背后的典故没有说出来，老外听了也不会明白的。
其实英文中有两个短语和“请君入瓮”的意思相近，直接用英文中现成的表达方法来翻译就行了。没有必要说"Please get into the jar, sir!" 让人听了摸不着头脑。
如果是做同传就更加没有时间解析成语背后的典故了。这时候应该意译，而不应该拘泥于原文。
give someone a dose/taste of their own medicine：to treat someone as badly as they have treated you：以其人之道还治其人之身
an eye for an eye： the idea that if someone does something
wrong, you should punish them by doing the same thing to them: 以牙还牙
An eye for an eye is no way to run a civilised justice
system.
孔子曰，“己所不欲，勿施于人。” -- Do not unto others what you would not have them do unto you。 -- Confucius
《圣经》则说，“Do unto others as you would have them do unto you.” (Matthew 7:12). - 你想别人怎样对你，你就应该怎样对别人。
道理是一样的。
其实"an eye for an eye"也是出自《圣经》。
另外一个短语"fight fire with fire"也是“以其人之道还治其人之身”的意思。
fight fire with fire: Use against your opponent the same methods he or she is using against you.