Wow, this could go in various directions:

• Author's Country of Origin (as the OP says below is what they intended with this request)
• Country Where Book was Originally Published (as suggested below by another commenter)

MAY I ADD:

• Country Where the Majority of the Plot Takes Place

An example where the answer is different for all 3 of the above is The No. 1 Ladies' Detective Agency books:

• Author's Country of Origin: Zimbabwe (even though he's Scottish, he was born in Zimbabwe and spent most of his childhood there)
• Country Where the Book was Originally Published: UK (the author spent most of his adult life in Scotland)
• Country Where the Majority of the Plot Takes Place: Botswana

Adding to this that it would also be great to be able to use this to filter! Esp when I'm trying to decide what to read for the Reads the World challenge :)

I love this idea!

I think "Country where book was originally published" could be really interesting, and maybe easier to record than the nationality of the author

Is this the author's country of origin?

I agree! I would also like to have the "Original title" and "Original language" fields.