I'm not 100% sure what causes the spacebar and prev/next frame commands to change from one language to the other, but for clarity, when you say you work with a swiss german keyboard, is this the keyboard on the computer? Is this an external keyboard? If so, is it an Apple keyboard?
If you are wanting the swiss german keyboard because it uses the characters, is that because they are printed on the keyboard or more that you are using english letters and remember where the swiss german characters lie?
The only thing I can recommend in the meantime, if you haven't done so already, is go to Tools and select 'Button List'. This will list all of the functions within FC Express and what their keyboard shortcuts are. For example, you can type a search for the word 'play' and it will come up with the list of functions that include play as part of their description.
If you had FC Pro, then you would have access to a similar keyboard shortcut window, but you would be able to customize it and make your own up.
The reason I also mentioned the external keyboard bit was because if you have a non apple keyboard it can sometimes create incompatibilities when using specialized software such as creative apps.
Hope that helps,