Within the 5 most crowded cities in the world, which country has the most languages used?
most crowded cities refers to MAX(Population); has the most languages used refers to MAX(COUNT(Language));
SELECT Name FROM ( SELECT T1.Name, T2.Language FROM City AS T1 INNER JOIN CountryLanguage AS T2 ON T1.CountryCode = T2.CountryCode GROUP BY T1.Name, T1.Population, T2.Language ORDER BY T1.Population DESC ) AS T3 GROUP BY t3.Name ORDER BY COUNT(Language) DESC LIMIT 1