What's the nationality mix in class like?

It is a fair question and a real effect, not a weird one to ask about. The mix varies enormously by school and by level.

Broad picture at Seoul university programs:

1. Chinese and Japanese students are usually the two largest groups, often 40 to 60 percent combined at the bigger programs.

2. Then a long tail: European, Southeast Asian, Central Asian, North and South American, Middle Eastern.

3. Western European and American students are a small minority almost everywhere — often two or three per class.

Where it differs: Sogang and Ewha tend to have a more Western-weighted mix. Yonsei and Korea University are large enough that classes are usually well mixed. Programs outside Seoul often skew more heavily toward one or two nationalities. Summer terms skew Western; regular terms skew Asian.

On your actual concern — schools know this. Most explicitly balance classes by nationality when they can, precisely to stop a single language group forming. If you ask the international office "do you balance classes by nationality", you will get a straight answer.

But the honest version: the default language of a class is decided by the students, not the school. In a well-mixed class the shared language ends up being Korean and sometimes English. In a class where half the room shares a language, breaks and pair work drift into it. That is human, and it happens.

What you can control: sit next to someone who does not share your language, on day one, and keep doing it. Most students sit with the people they can talk to easily, and that decision — made in the first week, half-consciously — shapes the whole semester more than the school did.

A class with one other speaker of your language is often harder than a class with ten, because with ten you are forced to choose, and with one you have a comfortable escape route that nobody notices you taking.