The benefit of using Single Programming language for both back-end and front-end is that it helps to remove Context Switching.
Context Switching means switching from one language to another. The effects of context switching are painfull:
1. If I am working on something, and I have to start doing something else, it can take ages before I am actually working on the new task.
2. Because I have to switch contexts multiple times a day, I feel that I cannot get anything done (often this isn't just a feeling).
Sorting the programming languages, I would list as listed by joy jooon.
Languages used for Standalone Development
Languages used for Web Development