That isn’t a proof. Synonyms can bolster the enumeration sans augmenting novelty.
I'm just on the thread following this idea: "The article seems to think that a word is untranslateable if there is no single word in the target language"
So we're talking about "translatability" of single words. Mapping multiple words of language X to one word of language Y is going to have some effect on translation.
Happy: Joyful, cheerful, merry, delighted
Or
Beautiful: Lovely, pretty, attractive
The only truly identical synonym I can think of is flammable and inflammable
But what joyful means to you likely differs from what it means to me, simply because we haven’t read the exact same literature and had the same conversations.