> I was wondering how the language information for babel has been curated
> over the years.

They are fairly recent (a couple of years).

> I’m guessing that typographic conventions, like hyphenation styles,
> spacing style, &c., are variously collected from the language’s institute
> for standard usage, leading style guides, and potentially uncodified
> typographic traditions known to babel contributors.

This is the idea, indeed.

> As for babel’s locale files, it appears that they are written by hand, yes?

Based on the babel and polyglossia ldf files, as well as
the Unicode CLDR. The original files were created automatically,
and then fine tuned by hand.