Hello,
me and my friend have noticed something quite weird in the English version of the little exam.
It never happened to us that we are asked to type a word in a category starting with the letter Z.
We have tried restarting the game many times to test this theory, in addition to playing the game itself many times, and we believe that there is something wrong here, that a letter might indeed be missing.
In the French version, the letter Z was chosen, but not in English.
Thanks.

What was the category just out of interest? There are animals such as zebra as I am sure you know beginning with Z, but generally Z, Q and x are not so easy for many categories as I am sure you know.

I think he means he has never seen any question where you have to type a word starting from z in any category.

Precisely what @Soundarya said.
I understand the difficulty of certain letters, and I thought of this myself, but letters like Q and X regularly appear compared to Z, so I don't think this was intentional and is rather some mistake in the English translation.

It is worth being checked out. Personally I would say X would be harder to find answers for.