1、We cannot legally conclude a peace treaty with Japan.
依照法律，我们无法同日本缔结和平条约。
nobody could legally drink on the premises.依照法律，没人可以在该场所饮酒。
~ sth (with sb) arrange and settle (a treaty, etc) formally and finally达成;决定;缔结（条约等）:Britain concluded a trade agreement with China.英国和中国签署了贸易协定.
2、They are nothing if not ambitious.
他们极为野心勃勃。
nothing if not：extremely; very极;非常;很:
The holiday was nothing if not varied.假日活动极其丰富多彩.
3、He is nothing if not a trouble-shooter.
他是个不折不扣的调解纠纷的专家。
4、Darkness released them from the last restraint.
他们趁着暗色摆脱了最后的束缚。
5、He really knew a thing or two.
（抱歉老师因为缺少语境，不太清楚这里想表达的意思，基本就是“略知一二”或“了解内幕”）
他还真地了解不少事情。
a thing or two1.真相；秘闻；内幕消息2.许多
knows a thing or two:十分精通；略知一二
6、We can not ignore our neighbors, only at our peril, can we ignore their distress.
我们不能对我们的邻国置之不理，如果我们不顾及他们的安危，就只能自身难保。
The lesson we learnt was that the state can interfere with the private lives of people only at its peril.我们学到的教训是国家在处于险境时能够干预人民的私生活。
实际上想说的是“我们学到的教训是国家要是干预人民的私生活就只会将自己置于险境。”
7、It is already four years since he was secretary general of the U.N.
他不担任联合国秘书长已经四年了。
若since引导的状语从句的谓语动词是终止性的过去时，则从句表示的时间是“从动作开始的那一时刻起”。如：
We have been missing them since they left here自从他们离开这里，我们就一直很想念他们。
若since引导的状语从句的谓语动词是持续性动词或表示状态的动词的过去时时，则从句表示的时间是“从那持续动作或状态结束时算起”。如：
John is now with his parents in New York, it is already three years since he was a teacher约翰现在和父母一起住在纽约，他不当教师已经三年了。
How long is it since you lived in Shanghai?你离开（没住在）上海多久了？
8、It is already many years since the Second World War.
二战结束后已经过去很多年了。
9、What he says can be taken as coming from horse’s mouth.
可以认为他说的话是可靠的。
straight from the horse's mouth:来自权威和可靠的消息；根据最可靠的消息来源；可靠地
What he says can be taken as coming from horse's mouth.可以认为他说的话是可靠的。
10、The British Prime Minister said, “They could throw every thing but the kitchen sink.”
英国首相说：“我们可以抛却任何事情。”
分析：https://idioms.thefreedictionary.com/everything+but+the+kitchen+sink
everything but the kitchen sink：Nearly everything one can reasonably imagine; many different things, often to the point of excess or redundancy.
指lots of different objects.
11、 The British Prime Minister said,“the policies of western countries are like ducks in a row.”
英国首相说：“西方国家政策是一致的”。
ducks in a row一致(像鸭子似的一个接着一个)