The country of registration makes very little practical difference.
It defines the flag (ensign) that [i]should[/i] be flown at the stern (i.e the same as the country of registry) but many people ignore that with no problem. All over the place I see Dutch registered boats with UK flags, SSR boats with Antipodean flags and all nationalities with the EU flag, which isn't a valid ship's ensign anywhere.
The Dutch registry (Kadaster) gives proof of ownership and (more important when you're buying) proves that the boat is not mortgaged. The the SSR doesn't - but one should have bill-of-sale papers of some sort to to show you own a boat wherever it was bought or registered.
Every registry requires that the boat is not on another registry.
My barge is Dutch and has more history than me so keeps its Dutch flag. The only language confusion is with the occasional person talking Dutch to me, which helps me learn it, but almost anyone who speaks Dutch also speaks English, so as Pete Clark says it's no problem.
Pete.