I am trying t find a birth register for my great grandfather Samuel F Keating who appears to have been born in Altona when it was part of Denmark. He was born in 1854 of Irish parents. I do not know why he was born in Altona. the census records for him vary. some say Cork, some say Altona Hamburg. In the 1921 census he put Denmark. I am really struggling to think where to go next to locate his birth certificate. Any suggestions?