Building an infrastructure for developing web-applications using multiple programming languages(Python Java C#)
I think rocco337's Service Oriented Programming is really a good idea.
But there's one slight downside of that particular approach.
Traffic between your services because of all these HTTP requests.
I heard amazon had suffered for it, But they managed it I guess because they are giant.
This one also has it's own downside. 
Just think this one as dirty and quick alternative.
Web application that I built recently was based on both python, php and bunch of C modules. 
The way I mingled them was using simple command line and shell scripts. 
And python works really great as a glue language.
so basically what you have to do is. 
A. Asynchronous approach. (When your module need more than few seconds to finish it's job)

open up a thread
run command line application (written in java, C# what ever)
show what ever view you want while waiting for result. 
when u get result from command line, let user reload or using ajax to refresh your view with result.

B. Synchronous approach. (Job is fairly simple)

run command line application
wait until you get result.
show user result view with result from 2

Good luck with your project!
I've searched for this on different places but I haven't found an exhaustive answer. Suppose we have separate modules written on different languages each of them realizes certain part of logic. We have not permission for recompile them to certain one language (for example using JPython).
I`m a real novice at this part of programming so it is hardly to find words describing this problem. It seems I try to find something like Maven but for multiple languages and for addition modules may be precompiled.
Is this theoretically possible?