I found a solution for your problem, i had the same problem but with a different language, Italian.
go to Control Panel
then click on Clock, Language, and Region
then click on Region
if you see the first line in Formats tab is
"Format: English(United States)"
then your are good
click on Location tab, and change Home location to united state
now click on Administrative tab
click on the first button "Copy settings..."
now u will see in "current user" your preferred language, which is English
check the two check-boxes at the bottom and click OK, this will change the Welcome screen and New user accounts to your Current user's settings.
your PC will tell you it need a restart, click no or later.
click on the second button "Change system locale". change the Current system locale to "English (United States)"
now restart your PC and enjoy an full English version of windows 8
this helped me get rid of the Italian language at the welcome screen, not sure English will still be the default language after you refresh your PC.