In my opinion, a modern developer should have deep knowledge about Object Oriented (OOP) and Functional Programming (FP). The programming language is something that must come later. Any good programmer should be able to switch from one programming language to another easily, if they follow OOP and FP. There are languages, though, that must absolutely be in the portfolio of a modern developer: Java, C#, Python and JavaScript. But be prepared to know also Scala, Kotlin, Swift, Go, Ruby, Rust and TypeScript.