So to prove your point that Lucifer = Satan, you quote a Catholic encyclopedia which just re-affirms the fact with no evidence, other than claiming that Jerome believed it to be so, but the trail goes cold for some reason (more claims without proof). You do realize that simply repeating something doesn’t make it true, don’t you?
And while it may be a convenient fact that things non-Catholics don’t like often turned up in the Middle Ages, that doesn’t make it any less true.
It’s also really easy for people who take passages out of context to distort them as you have done in this case. Isaiah 14 continues:
Satan never laid low the nations, the king of Babylon did.
It doesn’t get much more obvious than calling “Lucifer” a man, which Satan is suredly not.
Just keep reading Isaiah 14. You cannot reasonably claim that this is Satan unless you lift 3 verses out of the passage with no consideration whatsoever for context.