Just wrapped a long weekend in Seoul in November and as a tourist and, while English was not widely spoken from what I could overhear, it was present sufficiently in the tourist areas to get by. That includes visits to
Gyeongbokgung Palace and the Hanok Village,
Noryangjin Fish Market (including getting lunch in one of the restaurants, though that was one of the harder bits) and
dining at the Gwangjang Night Market.
We certainly did not randomly make friends and strike up long, involved conversations with folks on the street, but we did just fine on the visit overall. You might want a guide for some specific bits if you are the sort of visitor who wants to ask lots of questions at any given point in time, but we definitely didn't think one was necessary.
n.b. The link above is to my blog or to one which I am a regular contributor. FT rules require that I disclose that in the post.