想要更好的掌握你所学习的外语,去了解当地人所遵行的日常习俗和礼节
这个句子可看成It is a great help 4 the person后面的who is learning a foreign language修饰person,2 know some customs and manners 4 the people who speak it是实际主语,itis是形式主语,4 the people who speak it是修饰2 know some customs and manners .
整个句子可简写成2 know some customs and manners 4 is a great help.