But until you have the punchline the correct "free" translation of the question is "What do you call an elevator in English?". It's only after you've heard the punchline that you have to go back and re-interpret the question.
Which is why context-free translation is crap. The question itself is translatable, as is the answer itself. But the composition of the two translations is not the translation of the whole. This is equivalent to the translation of a sentence by compositing the translations of each of the words without taking into account their role in the sentence. "How do you call X in L?" is a perfectly valid and understandable English sentence, although less idiomatic than "What do you call X in L?" or "How is X called in L?". The context informs the translation.
