[nathan_long]

> In general language diversity at a company is a big negative

I agree. It really increases the difficulty of understanding the whole system. But it's a negative that has to be considered alongside potential benefits.

> If you have some developer that wants to write something in a new (for your company) language, or even worse goes off and does so without asking, because he wants to try it out, you probably want to fire that guy.

I get what you're saying; resume-driven development can ruin your systems. But at some point between "we wrote this new banking system in COBOL" and "every developer who knows COBOL and could maintain our old system is now dead", there needs to be an accepted way to experiment.