I see that you mentioned Swift, which is a great modern language. However, I think it's important to be open to other languages, even those that are less popular. There are many great languages out there, and each one has its own strengths and weaknesses.
I suggest you study other less popular languages, such as Julia, Go, Dart, and Rust. These languages are all new but mature and solid, and they offer a variety of features that you might find interesting.
Of course, the best way to decide which language is right for you is to try them out for yourself. See which ones you enjoy using and which ones are well-suited for your projects. There's no right or wrong answer, and the best language for you will depend on your individual needs and preferences.
Personally, I think Julia is the best language out there. It's fast, expressive, and has a large and active community. However, I also think that Go, Dart, and Rust are all great languages with a lot to offer.
I hope this helps!