VA uses the underlying Microsoft Speech engine for its voice recognition. Therefore I guess that you would need to add the English language information to your Windows setup and it would then allow you to change to "Microsoft Speech Recognizer 8.0. for Windows (English - UK)" after that train the setup and you should be ok.
On Windows 7, check the "Region and Language" section of the control panel.
There is a tab called "Keyboards and Languages". It says on this tab that languages you install can be used to support speech recognition. Of course that may change your entire windows interface to English, I cannot say!
I you manage to install the English language pack, goto control panel, speech recognition, and change the Language option to English. VA should work fine after that.
Regards,
Slan