In the french navy this rank is known as aspirant; in the german navy as fahnrich; and in the italian and spanish navies as guardiamarina. What is the equivalent rank in the Royal Navy?
I found both midshipman and cadet given by dictionaries in http://www.foreignword.com. From http://www.londonengarde.com/royalnavy.htm, it looks as though cadet is not a British rank. Cadet-Midshipman is an American naval rank and this may account for the dictionary translations. I'd go with midshipman