1. Go to Control Panel -> Site Pages -> Add Page. Fill out the Name: "Page1".
2. Click on Page1, then on Add Child Page. Fill out the Name: "ChildPage1". Don't click on Add Page button!
3. Click on Other Languages. Choose a language, and fill out the text field. There are n't the +, - buttons at the end of the panel.
If you click on Add Page before click on Other Languages, it works well.
I installed the core4 patch (2012. dec. 17)