Also, the star which falls from the sky is also mentioned in Revelation (IIRC), although maybe not explicity called Lucifer.
Something is translated correctly but narrowly - someone reads the narrow translation and misinterpret it when translating to another language. The same thing happen if you tell someone a story, and they tell it on. If I translate a text from norwegian into english, and then someone else translates it from english to, say, spanish .. then the spanish translation wouldn't reflect the norwegian text as good as the english one, as information WILL have been lost along the way.
Of course, you could always rewrite it into "Some people think that this is based on a Christian misunderstanding", however I don't think you'll find anyone presented with the facts arguing for the medieval view. :)
And even if the original text is talking about the king of Babylon, it is quite possibly using Venus as an allegory for the king. In which case, the later interpretation of it is perfectly legitimate. Alternatively, if they intepreted it as reffering to the fall of Satan, the translation may have been influenced by an independent tradition that Satan was the morning star. And look at Revelation, where you will find several references to falling stars, one of which may be Satan (I am no expert at interpreting Revelations) -- which might indicate a prior existence of a tradition to the effect that Satan is the morning star fallen from the heavens.
Anyway, to summarise -- there are other possible explanations than it being an inaccurate translation. It might be a perfectly accurate translation, according to the religious presuppositions of the translators. -- SJK