In an earlier post, I wrote about the benefits of listing your book in a small category on Amazon. Since the likelihood of making the top 100 in your category increases with fewer competition, your book will most likely fare better in a small category than a large one, where it is likely to get lost in the thousands of books listed.
However, I've recently discovered that certain categories do not exist in Non-US versions of Amazon. For example, both of my books 'Text Me, Guido' and 'Fifty Shades of Azzurri' are listed in the Comic Fiction category of Amazon.com, but unfortunately, this category (or an equivalent) does not exist on Amazon.co.uk, or any other Non-US version of Amazon. This means that the exposure of these two books is severely limited outside of the US. Therefore, if you have a book that you feel is marketable internationally, it may be wise to avoid the Comic Fiction category.
And for whatever reason, the Contemporary Fiction category does not exist in Non-US versions of Amazon, either.