Why is it that when you study a foreign language, you never learn the little phrases the let you slip into a culture without all your foreignness exposed?

• 在外语学习中，有一些不起眼的小词组，一时掌握，你就能融入一种文化中，而不会暴露你作为一个外国的痕迹。但为什么不去学呢？