Get it here.
This beta adds three localizations: Norwegian, Traditional Chinese, and Simplified Chinese (the latter two are still incomplete). Please let me know of any problems with these new localizations besides some missing strings in the Chinese ones. Backup behavior and resiliency has been improved. If you were seeing backup errors before, they should go away and backups should be happening (they were likely not happening at all on your machine, even on 5.1.2). The style of journals in the sidebar has changed a bit. There are also new versions of the Media Browser and the Google code, and some fixes for interacting with iWeb.