I'll try to answer the second part to the best of my ability, not knowing more about what sort of server problems you are trying to solve (http content? javascript PWA/SPA app? API server? chat server?)

- Python is a pretty popular language for server development. It does have some performance issues (including a global interpreter lock), so you would have to decide the trade-off of your time vs infrastructure cost.
- Ruby on Rails and Sinatra are both pretty mature at this point; less trendy but a known mix of positive/negative points. In particular, I have a pretty easy time making high-quality REST APIs and backing persistence store in rails than in a lot of other languages (but I'll also admit to a stigma against Python based on a prior work project I had to co-own and maintain)
- Javascript (via Node) isn't to be flippantly discounted. It isn't the best language and doesn't have the best tooling, but for a web application you likely will have front-end javascript anyways. You can also use Typescript, which usually is a net positive for productivity and maintainability (but I've hit a lot of issues lately with third party library type definitions)
- C# is becoming more compelling with the .Net Core work. In some ways it feels like a Java which was properly maintained by its vendor.
- I won't bash PHP, since its disadvantages are well known. But for quick prototyping web applications (without excessive javascript), a dev with PHP experience can work faster than in just about anything else
- For non-web applications, Erlang (or Elixir) as well as Go may be the best choices due to their inherent support for concurrency. I can't comment on their use for making web applications.
- C and C++ win in terms of theoretical maximum throughput and lowest latency/memory usage - but it requires time, knowledge, and skill to achieve that, and you likely care much more about business logic. I've seen experienced developers work months on a C-based server, only to beat its performance with something they wrote in a weekend in another language.
- Swift imho has yet to be proven for the server. If you love the language it may be worth trying for a project, but I wouldn't choose it for something on the critical path (yet)

Java still has huge benefits when integrating with third party technologies within a monolithic application. For example, when selling servers acting as on-premises middleware, Java enables you to use third party libraries and some glue code to make a plugin to theoretically support everything. You also have the benefit of being able to publish a programming API for others to extend your product themselves with Java code, something which may not be as easy to accomplish with compiled languages or if it requires the customer to learn something a bit more esoteric.

Java is somewhat unique in how easy it is to add third party code and dependencies to a project - scripting languages usually cannot match this as dependencies may also include native code. This is one area where Pure Java was a win, and is why a lot of distributed processing systems (such as Hadoop and Storm) often are written in and prefer Java.

Finally, I personally don't buy into JVM languages very much (Using JRuby/Jython to run portable code on the JVM is another matter). A different syntax doesn't solve the problems with the Java ecosystem or the JVM's resource usage or lack of inherent support for newer programming concepts. As soon as you branch out to use Java code, you lose a lot of the safety/immutability guarantees and features in the new compiler model. In return, you lose the ability for all of the Java developers to be able to understand and contribute to your code.