The Pittsburgh second person pronoun #yinz has come up here before (e.g., in this 2005 thread);
Now Ed Simon has a whole LitHub essay about it
(apparently an excerpt from his "The Soul of Pittsburgh: Essays on Life, Community, and History"),
tying it to the Glaswegian yins:

The city center of Glasgow, Scotland
—that iron-and-glass-forged, cobblestoned fortress of a hilly, rainy, foggy metropolis
—is bisected by the dueling high streets of Buchanan and Sauchiehall.
There are any number of landmarks to draw your attention if ambling down either of these bustling thoroughfares as the last squibs of Caledonian light fight their losing battle of attrition during a brisk November afternoon.
For six months in 2006, Glasgow was my home across the Atlantic, and I often spent those glum Scottish afternoons in precisely this sort of aimless wandering […] Glasgow, I thought, is kind of like Pittsburgh. And then, walking through Glasgow again, I hear it: “There was a couple other of yins as well.” What? […]
There is more than a spiritual congruence between Glasgow and Pittsburgh, as Kelman’s “yins” would indicate, the s that ends that word so perilously close a sibilant to the z in yinz and the words so nearly used identically.
For those unfamiliar with yinz
—though I imagine if you’re currently reading this book, you most likely know what it means, albeit it’s becoming increasingly rare in usage
—it’s simply the Western Pennsylvania second-person plural, the Pittsburgh equivalent of y’all down South or youse in Jersey and New York.

It is, admittedly to many outside the region (and to some within it), a strange-sounding word.
Where there is a certain sense in how you and all can be smoosh-mouthed over time into that southern all-purpose word,
yinz has a slightly alien quality about it, a combination of sounds that don’t quite make sense,
a shibboleth of identity to those who live in Pittsburgh and, apparently, Glasgow.
Because Kelman’s “yins” and the “yinz” you hear at Ritter’s Diner in Bloomfield, Gough’s Tavern in Greenfield, Gene’s Place in South Oakland or the Squirrel Hill Café literally have the same origin.

As any good Glaswegian would tell you, yin simply means “one,”
but though obscure, it’s actually the same with Pittsburgh’s most distinctive linguistic attribute.
Just as “y’all” is a compression of two other words, so does “yinz” come from you ones.
That phrase is a direct translation of the Gallic Scots, where the second-person plural is perfectly grammatically correct.

Calling it the “most salient morphosyntactic feature of local speech,”
Carnegie Mellon University rhetoric professor Barbara Johnson explains in her study
"Speaking Pittsburghese: The Story of a Dialect" (published as part of the prestigious Oxford Studies in Sociolinguistics series)
that “‘yinz’ was brought to America by Scotch-Irish immigrants… the descendants of Protestant people from Scotland and northern England.”

Because there are few famous examples of a Pittsburgh dialect
—Michael Keaton speaks with a wonderful accent, especially as the character Beetlejuice,
and outsider Nick Kroll does a fairly good imitation in the skit “Pawnsylvania” from his national sketch comedy show
—it tends to confuse people.
As an accent, Pittsburgh English may be centered in the city,
but today it’s more likely to be heard in the outer counties of Western Pennsylvania.
Linguistically it’s clearly a variation on northern Appalachian English;
yinz or some permutation is frequently heard in western Maryland, eastern Ohio and the West Virginia panhandle.

Within Pittsburgh, the accent has a curious aspect to it:
that vaguely twangy Appalachian pronunciation with all those loan words from Polish, Neapolitan and Yiddish,
making the dialect sound a bit like if somebody from Brooklyn was doing a really poor imitation of somebody from Kentucky, an urban Deadwood kind of talk.

Pittsburghese, Western Pennsylvania English or, technically,
the North American North Midland dialect
—however you choose to identify the accent, what’s unassailable is that such a way of speaking is strongly identified with the archetypal figure of the Yinzer.
As a Townie or a Southie is to Boston, so is the Yinzer to Pittsburgh.
...
He then goes on to discuss Yinzers at great length.
At any rate, the OED includes yinz under the α forms of you-uns (entry revised 2012):
2006 Yinz was drivin’ pretty fast back there.
Pittsburgh Post-Gazette (Nexis) 24 September h6
And the etymology is:
< you pron. + the plural of one pron. (see forms at that entry).
On the pattern of use with plural and singular reference compare discussion at you-all pron. With the formation compare also you-alls pron.¹, yez pron., yous pron., and also later we-uns pron.
#yins #yinser #pittsburgh #glasgow #pittsburghese
@pittsburgh
https://languagehat.com/yinzers/