Why would we need to know who each demon was an "ambassador" to? There are other pressing matters.
Anyway, the guy who wrote this book became a catholic ten years after publishing it, so I think that speaks towards the truth of the statement, which is to say it is probably not true, or otherwise not a meaningful summary of the abilities of the demon.
No. what you have read is most likely not true considering the author is deluded and not a source to be taken seriously.
Even in the chance that Belphegor did want some involvement with the country of France, the authors perception and interpretation of this is most likely incorrect given the author had likely no real occult understanding of the demons and how they are benevolent and have humanity's best interests at heart.