I have studied at BLCU and while there can be a lot of English speakers, you would be surprised they may not make up as big of a percent as you may think.

From my personal experience, when I studied during the summer it was about 25% South Koreans, 10% Japanese, 30% English speakers (mostly US and Canada), and the remaining are from rest of the world. During the winter however it was a bit different with about 40% South Koreans, 10% Japanese, 20% English speakers almost all from Australia, and the remaining from rest of the world. To be fair, this was at least 10 years ago so things might have changed.

With that said, I had friends from different countries and I quite enjoyed hanging out with non-English speaking students because then our only common language was Mandarin.