https://de.m.wikipedia.org/wiki/Büsingen_am_Hochrhein
This really frustrates me about Wikipedia because its like a totally parallel site and experience thats just right there and can even have conflicting information. Not helping the world as much as we think, but its so close to being able to.
I think your notification idea is good
It could look at number of sections, clusters of contributor activity, and then weigh that by character length with different weightings for each language
It might not be obvious to English speaking visitors as I suppose they don't pay much attention to the list, but visitors who speak multiple languages often switch between them to get the most information.
That's the case, at least when not on the mobile site; apparently the mobile site instead show the "best" version at the top of the list of versions, but I don't know how it is determined.
There's a template saying “this article could be improved with translation from $other-language.”
Germany introduced daylight saving time ("Sommerzeit") in 1980, but Switzerland only in 1981. In 1980, Büsingen used CET (like Switzerland), not the daylight saving time (like the rest of Germany). So, while there was only one summer season of deviation from Germany, Büsingen (pop. 1443) is listed separately in some time zone databases, eg the Common Locale Data Repository.
As so often, the devil is in the details.
I can give it a go, however my German skills aren't great.
A lot of Wikipedia is like this. The entries in different languages are not equivalents of each other.