“机器正在修理中”用英语怎么说？

楼上错误，机器是不会自己修理自己的，要用被动语态。
The machine is being repaired.机器正被修理。
更地道的版本是：The machine is under repair.机器正在修理中.

The machine is under repair

5楼的最好，不过是大多数人都能想到的，没创新。我有自己的理解。The machine is under reparation. If you' d like try something new, you can adopt this on

如果是警告语,就是: MACHINE UNDER REPAIR

如果是书面的: The machine is under repair.

REPAIR 在这里是名词, 代表修理.

The machine is under mending!

如果是警告语,就是: MACHINE UNDER REPAIR
如果是作文中就用 The machine is under repair.

还有如果要强调正在进行时的话，就要说The machine is being repaired.
都是地道的说法。