More can be written on such questions, of course. You might be interested in the "Calendars" FAQ wiki page. There are a couple of sections for time and calendars. Another page has stuff on number systems and calculations: "History of Mathematics" . Is it OK if I just point to the sections like that without listing specific postings? The question is pretty broad and there are a large number of postings.

I don't know of any previous discussions about why languages have not unified more.

This is not to discourage discussion. More questions, data, and debate are welcome. If you come up with a more specific question, please post.