While it may not be wise to do this it isn't unethical unless grading is competitive in some way. It potentially gives an advantage to those who take it later, but that doesn't necessarily imply a disadvantage to those who take it earlier.
But "grading on the curve" where some students must fail so that others can excel makes the calculation much different. In my opinion, however, that sort of grading is unethical in any case.
While I'm guessing that the exam is translated from one language to the other, that doesn't change the ethics of it, unless it is given to students in a language they can't be expected to know. Then again, it is unethical, as it disadvantages some students whether or not it advantages others.