Igor Karkaroff sounds like a Russian or Slavic name, and I always assumed he was an eastern European. But unlike e.g. Viktor Krum, Madame Maxime, and Hagrid, the character isn't portrayed in the books as having an accent, so he could be British of Russian descent.
In his youth, he was a Death Eater, a member of an organisation based primarily in Britain. Later he became headmaster of Durmstrang, a school in Scandinavia but which accepted students from as far afield as Bulgaria and possibly Britain.
Where was he from originally? Is there any canon evidence on this?