Best Language for AJAX, HTTP(S), server-side SQL, and Preprocessing?

I am working on a project that runs in a web browser. It gets all of its data from AJAX and/or HTML5 server events. It also needs access to the database which is also encrypted but uses SQL. It also, being a website/web-app, needs to be able to maintain some form of web-server filesystem for managing these AJAX and HTTP requests/responses. So I would like to only use one language as the backend for all of the non-browser provoked tasks. I can learn most languages pretty easily, so I really want a language that is scalable, can manipulate text simply, and has great performance speed overall. Not necessary but I think the language should be open-source and not-CPU dependent. Any suggestions?