We've done that on our team a few times, and for exactly the reason you've chosen Java over Perl in your example.

As a team decision, it was quite easily (and rightly) justified as an extra tool we could add to our skillset thereby being something extra that we could provide for our customers.

Now we never choose to explore a new technology on a time critical project. It would not look good if a project is dragging on some really basic bit of functionality because no one can figure out the correct syntax or something. But given that you can add the experience you gain on this project to something you can give back to the company, it's not a bad decision, as long as it's not a bad choice for that particular job.

The deciscion to stay with one technology or another, knowing that it's not necessarily the best fit is a whole other ball of wax that I won't get into.

elbieelbieelbie