Set the table, or lay the table?
Solution 1:
It's not so much that set is American and that lay is British - rather, that Brits use both forms more or less equally often...
...whereas Americans almost exclusively stick with set...
Personally, I find set slightly more "formal, dated" - but I suppose that's just because half a century ago, my mother always instructed one of us kids to lay the table. We were true peasants, so I always assumed set was a bit la-di-da (obviously it's not).
I think it's a given that since NGrams are drawn from written published sources, they'll tend to over-represent more formal usages. So I suspect that if I could compare formal/informal contexts (contracted I'll lay the table, as opposed to I will lay the table)), this might well support my gut feel about the difference (in BrE - obviously the concept is largely meaningless for AmE). But there simply aren't enough written instances to meaningfully compare.
Solution 2:
It is , and in my neck of the woods, London & home counties, still is, Lay The Table.
Set the table would probably get you a slap from my Grandmother in 1953!!!
Solution 3:
My mother (back in England) was a true "grammar nazi" when it came to my speech. She came from a British boarding school background and she always used "lay" when it came to the table. "Diana, it's time to lay the table." I have always thought of "lay" and being British and "set" as being standard in America (where I live now).