Changing a sites default language after running a long time

Hi guys,

I’m running a clients site, which has German as the default language. It’s done with RWML by Will Woodgate.
The client wants to change that to English. The point is that we cannot simply delete German, because Google has it’s search results, which are mostly German…

Is there anyone who knows how to get this default done? Or is it just as easy as putting en first in RWML