> it seems like I still won't be happy with it — judging by the wikis where the update is active, it's still too wide
I'm not sure what they looked like before, but I also visited a few of the localized wikis and ended up getting a horizontal scrollbar. I know that the theme on English Wikipedia is very old and not exactly responsive, but this is not something that happens there; I get no horizontal scrollbar. Everything is sized to fit within my window, except on certain articles containing wide tables or (unfortunately) multi-column reference sections, and even then, it's limited to those elements, which overflow, and the main article contents end up sized correctly. So I have to think that whatever changes they're introducing might actually be causing new problems...
I'm not sure what they looked like before, but I also visited a few of the localized wikis and ended up getting a horizontal scrollbar. I know that the theme on English Wikipedia is very old and not exactly responsive, but this is not something that happens there; I get no horizontal scrollbar. Everything is sized to fit within my window, except on certain articles containing wide tables or (unfortunately) multi-column reference sections, and even then, it's limited to those elements, which overflow, and the main article contents end up sized correctly. So I have to think that whatever changes they're introducing might actually be causing new problems...