That's strange, you sure you have actually checked your eShop "Settings" to make sure you've set them to English?
Likely you have, but in the eShop under "My Menu" and then "Settings", click on "View All" for the "Language" options.
But if that is (has been repeatedly) set to English, the only other place it should be is with the "System Settings" (the wrench icon), scroll over for "Console Information", and then "Set System Language".