Pascal, Delphi, C, C++, perl, Python, PHP, Java, JavaScript, Dart, Kotlin <- these are the languages I've built big systems in. That's approximately a new language every year and a bit.
Knowing a lot of languages helps you in picking up more languages pretty quickly, but it also means you only get to experience the language superficially.
When i started using Kotlin about a year ago, I decided to specialize for a change and only use Kotlin from then on. The result is that I write much better, cleaner and idiomatic Kotlin instead of just writing elementary Kotlin. I'm not an expert yet, but feel I'm making steady progress towards that goal.
Tl;dr; know a lot of languages, but choose one and specialize in it once you've figured out which one fits your style better - Jack of All trades, become a master of One.