>> You shouldn't jump from one language to another every few months, but you should keep a close eye on what other languages are doing and ask yourself if switching would improve the code you write.
Shouldn't that last sentence be "... if switching would improve the end product or service you are delivering." The focus should be on what people are paying you for. Better code doesn't always mean a better product, or be a smart business decision.
The two are equivalent in most cases. There's a relatively small set of problems where the choice of programming languages will have an effect on the product that doesn't come down to the code being more understandable and more amenable to change.
Pretty much speed is the only concern for the vast majority of web applications, it isn't really that big a concern for most web applications, and even then it's less about choosing the fastest language and more about limiting yourself to a still pretty broad set of "faster" languages.
Speed of development, or runtime speed? Language won’t matter for runtime speed except in the .1% of high load apps. In my experience speed of development will vary quite a bit based on language and quality of frameworks. I went from C# shop to Ruby/Rails and the pace increased substantially, though cultural differences are intertwined with language choices.
Runtime speed, as an example of one of the few considerations when choosing a language that isn't related to code quality and maintainability.
I agree though that it's not relevant for nearly all web applications (and even for those where it is, it doesn't require that everything is done in a performant language)
Sure, but the choice of language is rarely a factor in this, barring very specialized subdomains where library support is limited to a few languages. There's very few web applications that couldn't have been written in virtually any modern language.
I think ideally they are the same, but doing a re-write isn't cost free - opportunity cost as you're not doing feature customers care about, new bugs being created, old bugs re-appearing etc etc.
Shouldn't that last sentence be "... if switching would improve the end product or service you are delivering." The focus should be on what people are paying you for. Better code doesn't always mean a better product, or be a smart business decision.