"what kind of project would you rather write in this other language you know rather than in Perl?"

I can think of the following reasons to not use Perl. All of them have been reasons for me in the past to not use Perl.

• The environment it has to work on doesn't have the resources to have Perl. I've worked on Linux systems that only had 25 Mb of disk space, 8 Mb of RAM, and where installed from a single floppy disk. No way to cram Perl in there.
• Speed or memory usage is an issue. In such cases, I use C.
• There's a domain specific language much more suitable to solve the problem. SQL being an obvious example.
• Lack of enough Perl knowledge (or willingness to use it) in the rest of the team.
• Program needs to be distributed in an environment that may not have Perl. Hasn't been a reason for me in the last 10 years, but was before.
• Low level enough that it's easier to do in C than it would be in Perl.

Note that most of the reason have not much to do with the project itself, but more with the environment. But then, I've always said that most of the time you shouldn't pick a language based on the project you want to solve, but you should pick a language based on the people you want to do the project with.