Apple has changed their API, and removed the language code from the URL, so you should only the bundleId for the app you are looking for. For example:

http://itunes.apple.com/lookup?bundleId=com.yelp.yelpiphone

In addition, you can add the country parameter to the query, to get results for a specific country App Store.

For example:

http://itunes.apple.com/lookup?bundleId=com.yelp.yelpiphone&country=de

The description, user rating and other fields might change between different App Store countries.