因为过去分词后置定语的话,表示的是与修饰的中心词的被动关系,而在本句中并无这种关系,所以不行.可以改为表示主动关系的现在分词,即：
people living in different countries made different languages.the leaves fallen to the ground are cleaned.这句话可不可以认为是过去分词后置定语表完成呢？为什么上一句就不行呢？后面这句的原句是定语从句吧：
the leaves which have fallen to the ground are cleaned.
而完成时态是不能做后置定语的，所以说the leaves fallen to the ground are cleaned.这句话并不符合英语语言习惯