Somewhere inside that abstraction you’ll need to have the pieces of info that Spanish “leche” [milk] is feminine, that Zulu “ubisi” [milk] is class 11, that English predicative uses the ACC form, so goes on.

Of course you do. The beauty of abstraction is that these language-specific parts can be factored into generic language-specific components. The information you’re actually trying to convey can be denoted without any language-specific parts or exceptions and that’s the important part for Wikipedia’s purpose of knowledge preservation and presentation.

you’ll need people to mark a multitude of distinctions in their sentences, when writing them down, that the abstraction layer would demand for other languages. Such as tagging the “I” in “I see a boy” as “+masculine, +older-person, +informal” so Japanese correctly conveys it as “ore” instead of “boku”, "atashi, “watashi” etc.

For writing a story or prose, I agree.

For the purpose of writing Wikipedia articles, this specifically and explicitly does not matter very much. Wikipedia strives to have one unified way of writing within a language. Whether the “I” is masculine or not would be a parameter that would be applied to all text equally (assuming I-narrator was the standard on Wikipedia).

Even the idea of “abstract concept of milk” doesn’t work as well as it sounds like, because languages will split even the abstract concepts in different ways. For example, does the abstract concept associated with a living pig includes its flesh?

If your article talks about the concept of a living pig in some way and in the context of that article, it doesn’t matter whether the flesh is included, then you simply use the default word/phrase that the language uses to convey the concept of a pig.

If it did matter, you’d explicitly describe the concept of “a living pig with its flesh” instead of the more generic concept of a living pig. If that happened to be the default of the target language or the target language didn’t differentiate between the two concepts, both concepts would turn into the same terms in that specific language.

The same applies to your example of the different forms of “I” in Japanese. To create an appropriate Japanese “rendering” of an abstract sentence, you’d use the abstract concept of “a nerdy shy kid refers to itself” as the i.e. the subject. The Japanese language “renderer” would turn that into a sentence like ”僕は。。。” while the English “renderer” would simply produce “I …”.

A language is not an agent; it doesn’t “do” something. You’d need people to actively insert those pieces of info for each language, that’s perhaps doable for the most spoken ones, but those are the ones that would benefit the least from this.

Yes, of course they would have to do that. The cool thing is that this it’d only have to be done once in a generic manner and from that point on you could use that definition to “render” any abstract article into any language you like.

You must also keep in mind that this effort has to be measured relative to the alternatives. In this case, the alternative is to translate each and every article and all changes done to them into every available language. At the scale of Wikipedia, that is not an easy task and it’s been made clear that that’s simply not happening.

(Okay, another alternative would be to remain on the status quo with its divergent versions of what are supposed to be the same articles containing the same information.)