In France and Germany, both the novel and film were translated as "Interview with a Vampire".
French: Entretien avec un Vampire ("un" in French means "a").
German: Interview mit einem Vampir ("einem" on German means "a").

No, it was always "The Vampire."
When u say it out loud, there is literally no difference between "With A" and "With The" because the Th at the end of "With" blurs into the Th at the beginning of "The" leaving the " -e" of "the" (the Uh) sound, completely separate form the Th to our ears, giving the impression of it being the letter A (which is the word pronounced Uh")
There is literally no difference. Your mind fills in what it thinks it knows.

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WE'RE LOSING OUR MINDS!
It is a tale told by an idiot, full of sound and fury, signifying nothing
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