I wonder how many people will skip using Intl.ListFormat because it insists on Oxford comma in English. I know I’ll be skipping it. CLDR really missed the semantic nuance there—not that it could readily have included it. The problem is that it’s just too blunt an instrument. (Further reading: http://cldr.unicode.org/translation/lists, https://en.wikipedia.org/wiki/Serial_comma .)
Out of curiosity, why is the API's insistence on the Oxford comma a downside, seeing as it works for almost all lists? Is it due to overriding editorial preference - e.g. news orgs style guides?
The linked Wikipedia article is long, but goes into some depth on reasons and situations where it may or may not be desired. In American English it seems to be mostly a matter of preference and style guide, but in Australian English there is also semantic meaning to the comma, where it is possible in a carefully crafted sentence to convey quite a different meaning by the addition or removal of a comma; and unless there is semantic or possibly parsing value to be gained by the inclusion of a comma, it is broadly (though not universally) agreed that you shouldn’t.
As noted by narrowtux, not all English locales use the Oxford comma; en-AU also doesn’t, which mollifies me.
The simplest style of example I can think of is nesting conjunctions: “the difference between A and B, and C and D”. (This example isn’t great because it depends on nesting and has only two items in each list; but it’s the first that springs to my mind. There are others that don’t require nesting or only two items, though normally not quite so clear-cut.) Removing the comma or shuffling things around in any way would completely change the meaning of the sentence. This is the sort of subtle thing that some will miss when writing, but in speech it’d be very clear.
