Since 2016โ2019, aggregate monthly pageviews of Wikipedia's "Vital Articles" are down โ26% across eight major languages I sampled (en, es, fr, de, it, pt, ja, ar). The Vital Articles are an imperfect set, but they cover a much broader set of topics than my last sample set, and are widely replicated across wikis. (All of these wikis have at least 80% of the articles, making it more apples-to-apples.)
The decline isn't even across topics. Mathematics, physical sciences, and technology are down 43% to 85%; biographical articles and geography are down less than 10% in half the languages I looked at. The per-topic ordering (which have declined the most or the least) is nearly identical in every one of the eight languages.
Yes. Notably, the english version of wikipedia has a page of a list of bread.
The french version of wikipedia does not have that page. Further, many things are classified as bread in the english version of wikipedia, but as pastries in the french version.
I remember having an argument about this and I cited the english pages, and then they pulled up the french page and translated it for me. Lmao.
Yeah, the different versions don't have to be synchronised, and the standards for sources differ (outside of the big European languages, the standards are much lower and there's much more bullshit out there), and simply you can have one editor doing things the way they prefer on one wiki, an another editor with their preferences on the other one. Some of that can be a result of different local cultures or academic traditions (different terminology, different systems of classification, etc.).
Btw there's currently a project that's supposed to solve this, "Abstract Wikipedia", the idea being that you enter information that's language-independent and that can be converted into any individual language.
(It's really bad and won't work out.)