With regards to
Should you use two spaces after a period, or just a single one?
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.
How does the content on this site differ from the English Stack Exchange site?
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.