I think only very few people can be really proficient in more than 3-5 programming languages (at the same point in time). And with really proficient, I mean both a good understanding of the programming language semantically, being aware and keeping track of newer features in the language and having good knowledge of the standard library of the language (and potentially other common libraries). If you are not proficient in a programming language, you cannot work efficiently with it.

Personally as a backend .net developer, I consider myself proficient in C#, I know some basic SQL, and some basic TypeScript and JavaScript. Earlier on I have touched Basic, Pascal, Haskell, Prolog, Scheme, Ruby, Bash, Java and C. I have worked with several different programming paradigms and I have no doubt that this made me a better developer. Still, I don't consider myself a polyglot programmer. Even though I was proficient in Java and C earlier on, nowadays I would have to search basic things all the time if I'd work with those languages again. So that would not be efficient at all.

In my opinion, the concept of a polyglot programmer is only useful if it means a certain level of proficiency in multiple programming languages and that requires a lot more than understanding the syntax of those languages.