You can add any valid language code. Please see MSDN documentation for reference on CultureInfo class and language codes. http://msdn2.microsoft.com/en-us/library/system.globalization.cultureinfo(VS.71).aspx
Make Sitefinity work best for you.
Progress, Telerik, Sitefinity and certain product names used herein are trademarks or registered trademarks of Progress Software Corporation and/or one of its subsidiaries or affiliates in the U.S. and/or other countries.