MewBot and spaces
Now that you mentioned it to CodeCat, it's true that WT:NORM does not seem to have any rule for converting multiple spaces into one. FWIW, I'd support adding that rule to the policy, but for now I abstain as to whether MewBot should stop doing that.
I don't see any reason why it should stop now, it's close to finished on all Wiktionary entries already.
From a usability perspective, cases of two spaces after a period, where that sentence is followed by other text within the same paragraph, make the wikitext easier to visually scan in the monospace text presented by the editor, and thus should be kept. I would agree that cases of multiple spaces in other instances should be either collapsed, if followed by other text, or removed, if at the end of a paragraph.
Putting two spaces after a period is far from established practice though. I've never done it, and I wasn't even aware it was a thing.
Heh. That may speak to your youth. It's definitely a thing. There are whole tirades online about spacing after periods, with a general trend that older folks prefer two spaces, and younger prefer just one. C.f. the Carolingian reforms as they applied to writing: a single space between each letter, two spaces between each word, and three spaces between each sentence. Given that the "single space" in Carolingian terms just meant that the letters weren't all running together, we have modern block print as I learned it: letters distinct and separate, one clear whitespace between words, two clear whitespaces between sentences.
The practice of one space everywhere, even between sentences, appears to be a relatively modern contrivance. C.f. these two pages from Ben Franklin's Poor Richard's Almanack, or this page from the 1914 publication Library Jokes and Jottings by Henry T. Coutts, or this page from the 1894 book Benefits Forgot by Wolcott Balestier, or this page from the 1809 book The present state of Turkey by Thomas Thornton, or this page from Charles Dickens' 1853 book Bleak House, all clearly showing increased spacing between sentences than there is between words. HTML, XML, and other markup enforces single-spacing by programmatically collapsing adjacent spaces into one upon rendering. Modern fonts and layout engines theoretically handle kerning and such to adjust spacing between words and sentences, but many don't make any distinction, resulting in effectively the same spacing between words and between sentences. Two spaces after sentence-final punctuation, especially in monospace situations, can make it easier for a reader to visually parse the text, by clearly differentiating gaps between sentences versus gaps between inline words, including abbreviations that might be followed by a non-final period.
Eiríkr, maybe you could consider copying/editing some of your explanation into the "Usage notes" section of our entry about the space, which has none of that information.
That's an interesting suggestion. I'm chewing on how best to present the information within the context of the entry. I'll take a stab at it later, and the community can rework as appropriate.
It occurs to me that the information in my previous post might be too encyclopedic. There is the Wikipedia article, after all, and it goes into the details. @CodeCat, in case you're interested, there's a section on sentence spacing (Space_(punctuation)#Spaces_between_sentences), and even a whole article on sentence spacing (Sentence spacing), which I only just discovered thanks to Daniel's link (and then clicking through from there).
For the usage notes on the ]space[ entry, would it make more sense to just direct the reader to Wikipedia?
Yes, I suppose just directing the reader to Wikipedia sounds good enough.
Maybe with a quick note so that readers know what should they expect, like "there's some difference in the treatment of spaces between sentences, see more at (Wikipedia link)".