A few folks in North America have done this and it has been reported to work. I can't comment on it because I never attempted to do it.
You'll have to download some files and burn them onto a CD and load the CD into your Nav+ drive.
Thanks to John Hunter for adding this comment:
If you go to Babelfish's online translation service at http://babelfish.altavista.com/
and enter one of the web links provided, select language to translate as 'German to English', and hit the
translate button, you'll get a very useable english version of the web page.
Information and forum about this :
Tools : http://www.h-wu.de/_downloads/downloads.htm