Correcting the number/date formatting will probably be the more challenging, yet still boring, Job, I guess.

The AI revolution will take care of that job

Will it? Even when told to specifically use correct British English, LLMs make occasional mistakes and also get too eager and use it in code like CSS. With careful prompting, you can probably get pretty decent results with Claude or ChatGPT but it isn't perfect yet. I'm afraid that America has won another battle in this war.

As a programmer working in the UK I've never been asked to rewrite something into British English. I have been instructed to convert some old codebase to American spellings to "avoid confusion". Probably about 6 times in 20 years of professional programming and usually by some product manager based in San José following an acquisition. This is why the library exists I expect.

I've been dodging requests to "fix" British date formats in published articles to meet US reader expectations for a while now ...

Don't get me started on US calendars that have the weeks beginning on Sunday instead of Monday!

YYYY-MM-DD should aggravate everyone equally, switch to that

To be clear, I don't think the library would actually be used to accomplish this task. Rather I suspect a tounge in cheek reaction to years of tedious spelling adjustment disguised as urgent feature requests.

That's localisation