Is it common to have exam questions 'peer reviewed'? How common is it that exam questions, after being designed by the instructor and before being given to the students, are checked by a colleague in one's same institute, to make sure that they are appropriate and unambiguous and that their results are correct? Is this normally enforced by universities across the world?

I am asking whether there is a formal check required by the department; I am not speaking simply about instructors of the same course writing the exam collaboratively.

Motivation: anecdotal. A recent answer mentions "having [exam questions] checked / verified for quality, consistency etc". And I heard from a colleague from a country in the English-speaking world that in their institution something similar goes on: they prepare exam questions one week in advance, and then they are sent to be checked by a colleague. OTOH, this is completely unheard of for me in Italy --- the instructor designs the questions, then they are sent out to the students without any form of review imposed by the university (though the Italian system is somehow peculiar when it comes to exams.)
Yes; as mentioned in the UK it is expected that assignments (usually those greater than a certain proportion of the overall mark) is both internally checked and externally checked before being sat by students.

I have acted as an external examiner involved in the checking of the exam papers of another university. It is a valuable role that experienced academics can play in both improving the student experience, and the quality of the learning and teaching of an institution.

Another aspect that is also worth mentioning is post-exam error checking. In my department (some considerable time ago) we did an experiment of random error checking and to our astonishment, discovered that despite the diligence of the most experienced marker, things got missed. Our checking showed up whole missed script pages, ridiculous arithmetic errors in the final score and whole class transcription errors where spreadsheet cells were "off-by-one". As a result more regular clerical checks were done on everyone's marking and result recording to gain much in quality and student satisfaction.