* No Centralized Record: There's no single organization tracking every sale of the diary across all publishers, languages, and formats (hardcover, paperback, e-book, etc.).
* Ongoing Sales: The diary continues to be popular and is constantly being sold in new editions and translations.
However, we can say that:
* Millions of copies have been sold: It's a widely recognized and translated book, selling in the millions.
* It's one of the best-selling books ever: The diary is consistently on lists of the best-selling books of all time.
You can find estimates of the total number of copies sold online, but those are just that - estimates. It's safe to say that the number is in the tens of millions, if not higher.