Sounds like a great idea. Plain English (or any human language) is not the best way to store information. I've certainly noticed mismatches between the data in different languages, or across related articles, because they don't share the same data source.
Take a look at the article for NYC in English and French and you'll see a bunch of data points, like total area, that are different. Not huge differences, but any difference at all is enough to demonstrate the problem. There should be one canonical source of data shared by all representations.
Wikipedia is available in hundreds of languages. Why should hundreds of editors need to update the NYC page every time a new census comes out with new population numbers? Ideally, that would require only one change to update every version of the article.
In programming, the convention is to separate the data from the presentation. In this context, plain-English is the presentation, and weaving actual data into it is sub-optimal. Something like population or area size of a city is not language-dependent, and should not be stored in a language-dependent way.
Ultimately, this is about reducing duplicate effort and maintaining data integrity.