You may want to mention this next time
It terms of mapping the buttons, Windows doesn't distinguish between the plus key on a german keyboard, and the equals key on a US keyboard (US layout has no plus key, it's just a shifted state of the equals key): both trigger a WM_KEYDOWN message with a VK code of 0xBB. The ideal situation would be for Sublime Text to allow it to be bound via ether Alt+Plus or Alt+Equals, but for the moment buttons may only have a single name, so to bind to plus on a keyboard with a german layout, you need:
<binding key="alt+equals" command="noop"/>
This works for me if I set my layout to German.