Verified answer

Spending one week teaching English in Korea will make little or no difference for admission. Doing so only proves that you had the means to go to Korea and stay there for a week and the desire to use some of your time teaching English.

Teaching English to immigrants in your own US community on a regular weekly basis will look much better for admission as it shows a continuing commitment to serve your own community. Colleges want to see continuing commitments, not glorified vacations.