I would have translated "I have never visited France" as Je n'ai jamais visité la France, but apparently you could just as easily say Je n'ai encore jamais visité la France.
But what's the difference? Do the two sentences mean the same thing?
encore can be translated in this context as yet, implying that you intend to go one day.
I think a French speaker would rather say:
Je ne suis jamais allé en France → I've never been to France
Je ne suis encore jamais allé en France → I've never been to France yet