Check out Golang for the server, it's a statically typed language so it's fast and hard to introduce subtle bugs that can cause a lot of confusion. There is a ton of interest and mindshare moving towards Go and it's supported by Google so it's not going anywhere. Big projects like Docker and Kubernetes are written in Go.

For a web application I think most of the work will be in the frontend which basically means javascript. We've had a lot of success using Golang for the backend APIs and React for the frontend.