I once watched a Polish diplomat move seamlessly between English, French, Spanish, and Russian. I did not hear him speak Arabic, but he listened to the Arabic delegations without using the simultaneous translation headphones, so he had some degree of comprehension of that language too. He did use the headphones for Mandarin. Of course, I assume he was also fluent in Polish, although it not being one of the official UN languages I didn’t hear him speak it.
I suspect the linguist who “knew” forty languages had a familiarity with the grammar and basic vocabulary of those languages, but was no means fluent in them.
Japanese, he said, was an exception - he had had to study hard for seven years to attain the standard of an educated, well-read Japanese scholar, able to translate literary works into and from that language.
Literary translation is just about the hardest form of translation--to do it well, that is. You not only need to know the grammar and vocabulary, but you have to know the subtleties and the idioms of both languages as a native speaker does, so you can preserve the author’s tone and style. Plus, you have to be an accomplished writer in your own right. I can’t imagine someone being able to do professional literary translations in more than one pair of languages. (Maybe there are a handful out there who can do two pairs.)
There is no way in hell anyone can know forty languages well enough to do literary translations in all of them.