Amazon has various country-specific sites around the world. The UK has http://amazon.co.uk
Germany has http://amazon.de
Japan has http://amazon.co.jp
Canada has http://amazon.ca
and of course, the US has http://amazon.com.
Amazon eGift Cards for a specific country site are only redeemable on that particular store and cannot be redeemed at any of the others. Please make sure you buy the appropriate Amazon voucher where you or the intended recipient would like to shop.