The part I would agree with is that learning a new language != getting better at programming. When you learn a new language, you're increasing your breadth of knowledge - but most employers don't hire for breadth, they hire for depth. They want you to be good at the job they hire you for. And when you pick up a new language, you'll perform worse than on your existing languages, until you've had the practice to bring your skills up to where they were before.
Instead, spend time learning your language better. Most languages (even Python) provide different ways to accomplish the same task; try them all out, find out which is best, and most importantly, find out which is best for which tasks. Learn some libraries in depth. Write some actual code so you have something tangible on your resume - starting a project from scratching will teach you a lot that maintenance work at your employer won't, and even contributing some patches for an open-source project will teach you something new.
A big problem with many candidates is that their knowledge is very shallow: they'll claim to be an "expert JavaScript programmer", where "expert" means they can only use JQuery snippets they found on the web. And they don't even realize that their knowledge is shallow; they're completely oblivious to the depth of the subject until they meet someone who really does have deep knowledge (and even then, only rarely).