Local languages make it easier for a regional government/power to control a group of people.
More importantly, it dramatically reduces the amount of consumable information available to someone. Instead of being able to learn from tens of millions of books and billions of web documents, now you are able to learn from, if you are lucky, hundreds of books and thousands of web documents.
More importantly, it dramatically reduces the amount of consumable information available to someone. Instead of being able to learn from tens of millions of books and billions of web documents, now you are able to learn from, if you are lucky, hundreds of books and thousands of web documents.