With regards to
which has a so called "cross-site duplicate" at:
I'll refer you to an article used as an answer in one of the highest voted answers on the English site:
You'd expect, for instance, that anyone savvy enough to read Slate would know the proper rules of typing, but you'd be wrong; every third e-mail I get from readers includes the two-space error.
Note that Farhad did not say English here. He said typing.
And that's my whole point.
I don't think the rules of English language and grammar apply to mechanical (borderline typography, really) issues of how much physical space should go after a period.
I'm fine with this question existing on English as a variant applied to a different audience (rules wonks versus people who place words on a page for a living), but to argue that the rules of English language and grammar capture typography or the different technologies used to compose and render text on the page ... is a bit much.
This site focuses on writing style and technique
Whether you use one or two spaces after a period is at least as much a matter of writing style as whether you write poetry like ee cummings, in all lower case.
It is also a matter of editing and proofreading standards, which is explicitly on topic for this site per the https://writers.stackexchange.com/faq
The mechanical act of typing and typesetting is far more relevant to writers than English rules wonks.
So, in my opinion: this question is, if anything, more on topic here than on English -- but I don't think having the two perspectives on this matter from the two very different audiences is a bad thing, either.