Just master a one language, it doesn't have to be the latest or a modern one. and learn all the programming concepts and design patterns with related to that language.
Then learning new language is just a two or three days of work. you just need to map the concepts between the new language and the one you have mastered.
For an example,
I know what is singleton how to use and when to use. Usual singleton implementation is have (private?) static instance, private constructor and getInstance method.
so if i want to implement singleton using X language, i just google
private static variable in x language
private constructor in x language
getter override in x language
or most probably, how to implement singleton in x language
If you already know a language, then i guess JS/TypeScript/Swift/Kotlin/Go/Rust would be good candidates for 2023.