I know there is a unique card in Fluxx Espanol - Fiesta.
There are actually half a dozen unique cards in there, some which use La Fiesta and some which are just new for that version, like Siesta and Pastel Tres Leches.
Are there any unique cards in the German or Japanese decks?
Those versions were totally based on ours and have no new cards, just new art. Both are duplicates of Fluxx 3.0, though the German version also included 3 cards from 2.0 which they liked even though we'd decided to take them out (those being the Keeper hiding rules (Secret Data and Government Cover-up) and the Action for removing them (Security Breach).)
-- Andy Looney