An antonym is "a word or phrase that has exactly or nearly exactly the opposite meaning to another word or phrase". In WiktionaryZ, meaning is associated with what is called a DefinedMeaning. A DM is different in the way people think about concepts in that it refers to both synonyms and translations when you approach a concept from an Expression.
The technical problem is, when implementing antonyms in WiktionaryZ, are they still antonyms. Traditionally antonymy is considered within one language but because of the way WZ implements things, this is not true with in WZ.
Antonymy has it's own problems too. When a concept is considered the opposite of, this notion is often cultural. The problem then is, does antonym translate in the first place.