You can easily check any of them:

Google USA: google.com/ncr
Other Googles, just use the respective country codes, like google.co.uk, google.com.au etc. That would be English speaking markets.

See this also: http://www.seoptimise.com/blog/2006/...different.html

You can install Google or Piwik Analytics on your server to see what works in terms of sales.