Languages aren't all that different from each other. Most of the knowledge is shared between them (with a few exceptions like imperative vs. functional.)
Oh please. A "language" is way more than a way to define functions and add numbers. All modern languages like to rewrite the world: standard library, help system, build system, distribution system, FFI and so on and so on. It'd be great if these were standardized, but language authors love to NIH apparently. Moving to another "language" is a HUGE endeavor, unless of course you like to half-ass it.
Sure, but they're not that different, particularly if you've been around the block a bit and seen a bunch of these.
For a reasonable definition of the word productive, I've never found it terribly difficult to pick up and be productive in a new language. Sure, a year later I'll look back and say "man, I was so silly back then" but that's not the same as being useless. We routinely hire people at work who don't have experience in our primary language and it's never been an issue.
One of the things that irritates me the most about our industry is the fetishization of the difficulty of switching languages. In my younger days people would say that the syntax was too difficult to pick up. Now that people realize that's hogwash they've moved on to saying that the frameworks are too difficult to pick up.
Right, but there's nothing wrong with being a good programmer who needs to refer to the library docs more often. What's "oh please" is the notion that you can never be good at programming unless you've been using Perl nonstop since 1995. A Python programmer can pick up and become reasonably proficient in Go in a few days, for example.
Anyone familiar with any ALGOL-derived language could be productive, at a commercial level, in any other in a matter of days. Probably less these days with easily searchable API docs.
