does consistent colloquial language and regionally variable formal language make Hindi-Urdu unusual?
In most cases i am aware of (English, German, and Arabic) the formal language is consistent, but regional colloquial dialects can be unintelligible. But in Urdu and Hindi i have heard that the simple informal language is pretty much one language, but obviously they are written differently, and also the complicated words are completely different, Hindi takes them from Sanskrit while Urdu uses Arabic and Persian words.
Is Hindi-Urdu weird? Or is it just a coincidence that English, German, and Arabic are all the other way around?
The only other example i can think of is some other languages written in regionally variable scripts, like Farsi/Tajik, Mongolian, and a couple of others... But i know very little about these.
I think Hindi-Urdu is, indeed, a little weird and possibly unique.
The reasons for it are complex, and there are many, many hundreds or thousands of pages written about it with varying opinions.
One of the most significant comments about it that I've seen was, "there is no logic to it except the language-based political games of 1900 to the 1940s". This, I think, is more important than any linguistic reasons.
And indeed, I think that to understand it properly it would be necessary to look in depth at both religion and politics as well as the history of that part of the world over the last hundred years and in fact very much longer.