On a fresh install (13.04) I see a strange mix of languages in Software Center
The menu (like my system language) is in English, but the descriptions are in German. I want the descriptions in English too.
I am using a german keyboard and have German installed too (for giving support to students with German as system language :-))
In system settings I have moved German below English - so it should be ignored, I have logged out after that.
I have cleared the "Software Center Cache" with Ubuntu Tweak. The picture remains the same.