两句中的as引导的都是定语从句.
第一句中的as代指pen,在定语从句中作bought的宾语.
第二句中的as代指dialect,在定语从句中也用作宾第,但二句中的定语从句中省列掉了speak with,as做with的宾语.
第二句补充完整了就是：
So people from the mountains in the southeastern USA speak with almost the same dialect as people in the northwestern USA speak with.
希望可以帮到你.