出国留学背景的人对标的是educated population，不是文盲。educated population有30000以上词汇量稀疏平常。英语文盲靠500词汇是不可能生活的，而90%以上美国人上过高中，所以说美国90%以上的人有大于20000词汇量是没问题的。美国农民不是uneducated people，In 1960, 40 percent of the rural population ages 25 and over had completed high school; by 2019—59 years later—that increased to 87 percent.
所以词汇对二语者还是要背的
Educational attainment in the United States - Wikipedia.
USDA ERS - Rural Education.