I was able to find this information from the official support documentation for Siri: http://support.apple.com/kb/ht4992
Siri understands and can speak the following languages:
- United States (English, Spanish)
- United Kingdom (English)
- Australia (English)
- France (French)
- Germany (German)
- Japan (Japanese)
- Canada (Canadian French, English)
- China (Mandarin)
- Hong Kong (Cantonese)
- Italy (Italian)
- Korea (Korean)
- Mexico (Spanish)
- Spain (Spanish)
- Switzerland (French, German, Italian)
- Taiwan (Mandarin)
But I don't think it has been updated as of iOS 7.1 (the page shows Last Modified: Sep 18, 2013). So...
What are all the languages that Siri supports as of iOS 7.1?
Is there an changelog available showing languages added in each version right from the beginning?