Is it unethical to poorly translate an exam from Dutch to English and then present it to the English speaking students?
There are two different questions in here that are mixed up: one about whether the Dutch and English exams should be identical and one about exam quality.

Regarding the first question: I fail to see why this should be unethical. On the contrary: It seems very good that the standards on what you are supposed to know are the same. After all, you get the same degree.

Regarding the second question: Also here, the answer is obvious: Of course, exams need to be of good quality. If that is not the case, sure, this is a problem to be addressed. But that has nothing to do with the question of whether they are a translation or not.