Perl has a Poland Problem. The customary file extension for Perl files is *.pl. This worked well until Apache introduced content negotiation and the convention to add a language code as file extension. It had index.html.en, index.html.de, for example.
index.html.pl is where the problem started and the reason why the officially recommended file extension for Perl files used to be (still is?) *.plx.
I don't have the Camel book at hand, but Randal Schwartz's Learning Perl 5th edition says:
"Perl doesn't require any special kind of filename or extension, and it's better not to use an extension at all. But some systems may require an extension like plx (meaning PerL eXecutable); see your system's release notes for more information."
It should have been an Apache problem, yes. Not only did it turn out that at least the language negotiation part of content negotiation wasn't the best idea but the way Apache handled it was problematic apart from the pl problem. In the end the Perl community took the issue upon them, so historically I'd say it was a Perl problem (of choice).
index.html.pl is where the problem started and the reason why the officially recommended file extension for Perl files used to be (still is?) *.plx.
I don't have the Camel book at hand, but Randal Schwartz's Learning Perl 5th edition says:
"Perl doesn't require any special kind of filename or extension, and it's better not to use an extension at all. But some systems may require an extension like plx (meaning PerL eXecutable); see your system's release notes for more information."