Now I have work with PHP and ASP.NET quite a bit and also played around few other language for web development. I am now at a point where need to start building a backend platform that will have the ability to support a large set of applications and I am trying to figure out which language I want to choose as my core language. When I say core language I mean the language that the majority of the backend code is going to be in. This is not to say that other languages won't be used because my guess is that they will but I want a large majority of the code (90%-98%) to be in 1 language. While I see to benefit of using the language that is best for the job, having 15% in php, 15% in ASP.NET, 5% in perl, 10% in python, 15% in ruby, etc… seems like a very bad idea to me (not to mention integrating everything seamlessly would probably add a bit of overhead).

If you were going to be building a large scale web platform that need to support multiple applications from scratch, what would you choose as your core language and why?