Write SQL query to solve given problem: Calculate the percentage of the surface area of all countries that uses Chinese as one of their languages.. Keep the solution inside sql tag ```sql [SQL-Query] ```
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