I have heard the following (German spellings):Katinka KajuschaCatherineZeta Jones was called Kato or Katto (unsure spelling) in "Catherine the Great". I am not sure if that is a Eastern European nickname for Katerina. "KATÓ" is in the BtN-list. That might be the name that I am thinking of.
CatherineZeta Jones is welsh. It is common to form nicknames ending in "o" in welsh usage. Kato is an example of this as is Eddo for Edward etc. Nothing to do with the Balkans.
Thank you Ivayla. That is what I meant to say. I should have been more clear on that. But Blodwen's input about Welsh naming practices was interesting nevertheless.