The Google side of things should now be displaying in your preferred language, which is half the battle. Wolfram Alpha doesn’t really have any language settings yet, so you’ll just have to put up with English on that side of your screen.
If Google isn’t properly localized, first make sure your browser actually knows what your preferred language is!
In Firefox, go to Tools->Options->Content->Choose and make sure your preferred language is at the top of the list. In Internet Explorer, try checking Tools->Internet Options->General->Languages. If you’ve got a different browser, you’re on your own — unless some kind soul leaves a helpful comment
It’s difficult for me to see what things look like from different countries, so please, let me know how things look to you!