The first answer has some great information! Some other things to consider would be in relation to why you want to go oversees and if you have a preference of where you would like to go.
Attending a college with an ROTC program for any branch of the military has some great benefits of a military career and being able to teach on foreign bases around the world. Typically, you get at least your room and board paid for through ROTC and you have a year or two to make a decision to continue toward a military career or leave the ROTC. If you decide to join, you can often join reserves and put in some of your required time while still in school and then be commissioned upon graduation having most, if not all, of your education paid for then continue both goal paths.
If religious reasons are your motivation to teach oversees, check with your church for affiliated missions and education programs that may provide you the opportunity to study abroad as well as a sort of "internship" with others teaching around the globe.
My last bit of advice would be to determine if a degree focus toward languages or toward early childhood education best meets your goals. There are several universities that can meet these needs depending on if you want to stay close to home or travel away. While a English as second language (ESL) certification is important in the USA, that certification may not be of any help depending on your career destination.
Good luck in your adventures!