On mine I have loads of language options, are you looking in the right place? System settings > Language and input > Language.
Spanish and Russian are included in the list. If they're are not in yours then it would seem Rogers removes stuff from there handsets.
One way round it would be to flash an unbranded firmware. I'm not sure what there is out there for your version of S3, so you would have to do some research to find out. best place to start looking would be on xda-developers.com http://forum.xda-developers.com/forumdisplay.php?f=1563
you'll find all the info you need on there and guides on how to do it.
Hope this helps.