I had the problem, that I wanted to sync multiple calendars using the google mobile sync to my iPhone. I am located in Austria, so my language settings are German. If you follow the instructions here you will get a device not supported error message. I found on the web that you have to click on „Change Language“, change the language to „English (US)“ and then it will work. This is a bad bug on m.google.com/sync which is not easy to go around if you don’t have the information I found on the net, so Google please fix that.
(click on „Change Language“)
(Select the device and then select the calendars to sync)