This makes me despair a little. Try speaking English in Miami and see how far you get! You'll find no problem navigating ICN, it's one of the world's better organized airports and staff are consistently polite and courteous.
Just use the normal techniques when speaking with non-native English speakers. Don't speak loudly, it doesn't help. Use short, simple, uncomplicated sentences. Avoid jargon. Speak more slowly than usual.
And if you want airports where people really don't speak English, try Russia.