@VancouverM:
I'm glad to read that you've successfully changed the language by replacing the corresponding module in the file navboot. I was just about to test that myself (I'd like to replace French)

On the other hand you're writing that the cluster still has the original language, which at a second thought sounds reasonable, since the nav unit doesn't provide the cluster with the messages to display (as I understand the design - correct me if I'm wrong at this point)

The bad news is that if it's true that the cluster only gets a command telling it to which language to switch, there's no way but to recode it to use another language setup.

On the other hand, if it is only a command that is sent out from the nav unit, it might be very well coded into the navboot file as well, which might be changed. In my preferred setup that would mean that when I switch my European nav unit from D (German) to GB, I'd like it to have the US female voice and the US menu items (it's ok for the cluster to be in GB mode then.) I would then like the third option F (French) to switch the nav unit to the US male voice with the US menu items and the cluster should switch to GB.

So, if someone with the needed insight could find out how the cluster switches its language when you select the corresponding menu item on the nav unit setup screen, one might be able to "tune" that, too...