Database: card_games
Question: What percentage of Japanese translated sets are expansion sets?
SQL: SELECT CAST(SUM(CASE WHEN T2.language = 'Japanese' THEN 1 ELSE 0 END) AS REAL) * 100 / COUNT(T1.id) FROM sets AS T1 INNER JOIN set_translations AS T2 ON T1.code = T2.setCode WHERE T1.type = 'expansion'