Each format of each edition is its own product, so each needs its own ISBN: the ebook, the paperback and the hardcover, in every language.
- Print books need one. On KDP you can use your own or KDP's free ISBN, which works on Amazon only and shows "Independently published" as the imprint.
- Ebooks don't need one on KDP, Apple Books, Kobo or Google Play, which give them their own IDs. Your own ISBN names you as the publisher and stays the same in every store.
Each book says where its ISBNs come from, on its page under What you're publishing. A book on KDP's free ISBNs needs none to get: KDP gives each print format one as you set it up.
ISBNs come from the national agency where you, the publisher, are based. Some are free, such as Poland's e-isbn.pl and ISBN Canada; others sell single numbers and blocks, where a block of ten often costs less than two singles.
What you get: the formats still without a number, how many to get, and the cheapest way to get them from your agency. The studio never buys or registers numbers for you.