[artfulhippo]

You can't actually be a Master of only 1 language.

This applies to human and computational languages. Consider that English derives from French, German, Latin, Greek, etc. Without knowledge of the root languages, you can't actually master English.

And beyond polyglot is "polyparadigm". Knowing 7 languages in the same paradigm makes you an expert in a particular style of programming. But True Mastery means transcending style.

With that said, most are better served by gaining proficiency communicating with (managing) people than mastering programming.