I’ve read this response three times so far without completely understanding why you’d say that I “underestimate the problem” here, when you and I seem in fact to be saying the same thing.

If the project at-hand was originally and substantially developed in C++, then it is absolutely correct to say that a substantial body of experience in that language might be called-for in order to properly assuage the business risk that the person you just hired, in fact, does not know what he is doing and is too-green to know it.   (May I please have a quick count of how many heads are bobbing up and down right now, please?   Thank you.)   I rest my case.

The key word is that ... no matter what language(s) were used to develop the software, the project must have an assured service-life “for years.”   C++ is a great language .. so is Perl .. so is Python .. so is PHP .. so is .. well .. ;-) Java is out there, too ..   The multi-million dollar decision was made some time ago, and it was in fact not (or maybe it was? ...) a lousy decsion, but ... “We are here now, en-ter-tain us ...”

The people whom you call “easily hired” are not the ones you really want:   the people who have just one-or-two languages under their belt.   Monster.com will serve up people like that by the hundreds.   The people you really need are the ones who can truly set a programming-language tool in context.   And who can set a project in similar context, no matter what language(s) were used so-far in its construction.

Indeed, the people who can un-flinchingly approach a project that was done in a language they had never seen before, and who are not bluffing in their confidence, and do it because they have encountered so many technologies before.