On existing projects, consider the global effort to change from origin/master to origin/main. The cost of being different than git convention and every book, tutorial, and blog post. Is the cost of change and being different worth it?

I'm not sure why MSFT decided to change these codes in the first place. While it might have been a noble goal to follow the IETF standard (though I'm not really familiar with this), the old codes were already out there, and most developers don't benefit by the new codes, nor care about what these codes are called (a code is a code). Just the opposite occurs in fact, since now everyone including MSFT itself has to deal with two codes that represent the same language (and the resulting problems). My own program needs to be fixed to handle this (after a customer contacted me with an issue), others have cited problems on the web (and far more probably haven't publicised theirs), and MSFT itself had to deal with this in their own code. This includes adding both codes to .NET even though they're actually the same language (in 4.0 they distinguished between the two by adding the name "legacy" to the full language name of the older codes), adding special documentation to highlight this situation in MSDN, making "zh-Hans" the parent culture of "zh-CHS" (not sure if it was always this way but it's a highly questionable relationship), and even adding special automated code to newly created "add-in" projects in Visual Studio 2008 (only to later remove this code in Visual Studio 2010, without explanation and therefore causing confusion for developers - long story). In any case, this is not your doing of course, but I don't see how anyone benefits from this change in practice. Only those developers who really care about following the IETF standard would be impacted, and that number is likely very low. For all others, the new codes are just an expensive headache. Again, not blaming you of cours

I feel the pain. It is a normal thing that standards do evolve over time, though, and our software needs to cope with it.

I'm not sure why MSFT decided to change these codes in the first place. While it might have been a noble goal to follow the IETF standard (though I'm not really familiar with this), the old codes were already out there, and most developers don't benefit by the new codes, nor care about what these codes are called (a code is a code).

One of the primary tasks of engineers is to minimize complexity. JSX changes such a fundamental part (syntax and semantics of the language) that the complexity bubbles up to everything it touches. Pretty much every pipeline tool I've had to work with has become far more complex than necessary because of JSX. It affects AST parsers, it affects linters, it affects code coverage, it affects build systems. That tons and tons of additional code that I now need to wade through and mentally parse and ignore whenever I need to debug or want to contribute to a library that adds JSX support.

This balancing act needs to take into account project complexity (size, distribution, etc.), uncertainty (risk, innovation need, etc.), and the cost of change at the project level and for each major component.

Compounding the problem of iteration disguised as oscillation is the cost of change.