I explicitly will not hire any programmer who knows only one programming language (C and C++ count as 1 for that score.) Learning a different programming language introduces you to alternative ways to think about problems and solutions. Lisp or Scheme, Ada or Eiffel, COBOL or MUMPS, all provide a different perspective on software design, coding, test and integration.
Too many hiring managers play "buzzword bingos" in search of "flying purple unicorns," candidates whose buzzwords match their current search list. Sure, you can make a living chasing buzzwords that way, with a combination of (primarily) resume engineering and (secondarily) training. And some people who do this are actually pretty good developers. But many more don't know how to apply the technology, they're just able to produce toy programs learned from " for Idiots" who produce the stuff documented on http://thedailywtf.com/ But the people I want are those who can think creatively about a problem, using more tools than just one hammer, and who can learn new stuff on the job. What's the half-life of a technology these days, 3 years?