Who said so? You could have umpteen number of regional languages here on IRI. Just start updating the site with your version of regional language.
But, FYI Hindi isn't a regional language. And, like you already mentioned, it is one of the official languages used in IR( I will just talk about IR's perspective, as this site is all about IR). Now, the site owner(Moderator Sir) already announced to have information in multiple regional languages. Where is he at fault?