Question: Calculate the percentage of the surface area of all countries that uses Chinese as one of their languages.
SQL: SELECT CAST(SUM(IIF(T2.Language = 'Chinese', T1.SurfaceArea, 0)) AS REAL) * 100 / SUM(T1.SurfaceArea) FROM Country AS T1 INNER JOIN CountryLanguage AS T2 ON T1.Code = T2.CountryCode