I'd recommend you to take a look at Java and Kotlin, the first due to the number of companies that actively use it in your products. Kotlin is gaining adept since it is fully compatibly with the Java ecosystem but usually requires less code to do the same (ignoring other benefits of the language). Another benefits of the Kotlin is that it is in fact multiplatform, where you could use the same syntax to code for mobile, web and backend applications. The drawback of Kotlin, is the number of open jobs that exists currently compared to Java, but I pretty sure that it will change in the near future.

I will highly recommend Kotlin. I have worked with all three intensely and so far the development speed and simplicity is the best with Kotlin. Kotlin supports coroutines out of the box. Now, it isn't something that can't be implemented in other languages but Kotlin makes it super easy to work with them. Kotlin has a bit of learning curve, so, by the time you can actually use it idiomatically chances are that you will get proficient in Java too. But once you get it, you get it, then there is no other language ;) Kotlin is backed by Google and Jetbrains team so you can expect latest programming features and good community support.