Languages simply don’t agree on how to split the usage of words. Or grammatical case. Or if, when and how to do agreement.
Just for the sake of example: how are they going to keep track of case in a way that doesn’t break Hindi, or Basque, or English, or Guarani? Or grammatical gender for a word like “milk”? (not even the Romance languages agree in it.) At a certain point, it gets simply easier to write the article in all those languages than to code something to make it for you.
I don’t know what the WMF is planning here but what you’re pointing out is precisely what abstraction would solve.
If you had an abstract way to represent a sentence, you would be independent of any one order or case or whatever other grammatical feature. In the end you obviously do need actual sentences with these features. To get these, you’d build a mechanism that would convert the abstract sentence representation into a concrete sentences for specific languages that is correctly constructed according to those specific languages’ rules.
Same with gender. What you’d store would not be that e.g. some german sentence is talking about the feminine milk but rather that it’s talking about the abstract concept of milk. How exactly that abstract concept is represented in words would then be up to individual languages to decide.
I have absolutely no idea whether what I’m talking about here would be practical to implement but it in theory it could work.