I love when I learn something new, like today when I learned that the Google Rich Snippets Testing Tool only works with English data but Rich Snippets in the main search results works in many many languages.
A Google Webmaster Help thread had one user complaining that his rich snippets were not working when he switched the dates to French from English and yet the dates in the Rich Snippet Tool were only showing the dates in English.
Jack from Google explained that the testing tool only works with English dates but the search results themselves will show the proper language.
He showed an example query of [ben folds]:
So if you run into this issue, now you know why.
Forum discussion at Google Webmaster Help.