What is the annual average number of sets that were released between 1/1/2012 to 12/31/2015? Indicate the common langugage of the card.
AVG(id); releaseDate BETWEEN 1/1/2012 AND 12/31/2015; the common language refers to MAX(COUNT(language))
SELECT (CAST(SUM(T1.id) AS REAL) / COUNT(T1.id)) / 4, T2.language FROM sets AS T1 INNER JOIN set_translations AS T2 ON T1.id = T2.id WHERE T1.releaseDate BETWEEN '2012-01-01' AND '2015-12-31' GROUP BY T1.releaseDate ORDER BY COUNT(T2.language) DESC LIMIT 1