There are many foreign areas in Bangkok. I think everyone knows about Chinatown near the old part of this city but many people dont know that there are also many small foreign areas in Bangkok in Sukhumvit, Silom and other busy cenral parts of the city.
One of the favorites of mine is the Korean Area (I think called Korean Town??? not sure) on Sukhumvit. It is betwenen Sukhumvit Soi 12. Food there is very good with a great selection of Korean bibimbab, BBQ grill and also fried chicken. Many of the shop brands are from Korea, so you know it will have the authentic taste that you can expect from a real Korean restaurant and not fake Thai-style or Western taste.
The location is simple: at Sukhumvit Soi 12, between Nana and Asok BTS Station. I think the best way to get there is to take the BTS train to Asok and use skybridge to access to Times Square tower. Then, you can walk down from inside the tower and go down the street to Korean Town. Make sure to enjoy Bibimbab for me!