Maybe it doesn't make sense, but this is what it says on the "supported languages" page:
Authors and publishers can upload and sell books to customers in the Kindle Store worldwide which are written in these languages:
• English
• French
• German
• Spanish
• Portuguese
• Italian
We're unable to support character-based languages or entries (including Eastern European characters, Japanese letters, Russian characters, etc.). We are working to add this option in the future.
I should add that this list of languages is also on the very first page for KDP, so it's not like they're being deceptive or obscure about it.