I have taken the Alloy tech project and started from there. When I changed the default language to Swedish, I also changed the fallbackLanguage to Swedish.
It took me a while to figure out why the edit mode sometimes (most of the time) doesn't load in any other language but English. Admin mode works normally, but edit just doesn't load the main part (the upper menu is still there).
I get an error in Chrome: "Cannot read property 'confirmation' of undefined. In FF, I get "_12f2.buttons is undefined".
I have switched back the setting to fallbackLanguage="en", but it either shouldn't be exposed as setting if it's not really changable or it shouldn't crash the edit mode.
Hope this helps someone else.
We're having this problem too, any fix for this yet?