Is the Google Calendar Jewish?

Yes, we found public Hebrew calendars that will make your Google Calendar Jewish.

To add them to your Google Calendar, select Other Calendars on the left and click on Add, then choose Add by URL and copy one from below, then click the Add Calendar button.
Copy the URL below (from the Google Help Forum 11/26/09 courtesy of a user named Ephraim):
Public Google calendar -- Hebrew date. (It excludes times, holidays, and Torah portions so that it can be used together with other calendars in various locales)
http://www.google.com/calendar/feeds/qhasa5afg633voo8j26mf1ntjs@group.calendar.google.com/public/basic
Public Google calendar -- Torah Portion.
For the Diaspora (outside Israel): http://www.google.com/calendar/feeds/olv18cdaciiflov66ah3qlkntk@group.calendar.google.com/public/basic
For Israel: http://www.google.com/calendar/feeds/tuojqh14bvmhomns7dod9fqci8@group.calendar.google.com/public/basic
Public Google calendar -- Daf Yomi.
http://www.google.com/calendar/feeds/v5bvdts4vlfhd2dfgdairv9t94@group.calendar.google.com/public/basic