‘Lucifer’ or its equivalent does not appear in the original Hebrew. The reference is to Nebuchadnezzar.
I must confess that this is very interesting, I had never heard these verses applied to Nebuchadnezzar, but it makes sense considering the previous part of the chapter. One thing that fascinates me about Scripture is how some times there's more than one meaning to a word or passage. For example, matzah referring to the bread the Hebrews did not have time to let rise, or as an image of Messiach. Is it possible that Isa. 14:12 has more than one meaning?
When I want to check the Tanakh, I go to jewishvirtuallibrary.org. In the book of Yeshayahu, chapter 14 verse 12 I read “ How art thou fallen from heaven, O Lucifer, son of the morning! how art thou cut down to the ground, which didst weaken the nations!”. It sounds just like my King James! Do you have a better, I mean more accurate, English translation of the Tanakh?