Your friend in Vietnam probably had this yearning lust, this undying compassion, to secretly live life as a Kathoey. He didn't feel that his friends and family back home would ever accept it so he told them he was going to teach English in Vietnam then cut off contact.
Of course you need to know Polish to teach English as a foreign language in Poland. As a matter of fact, to teach English as a foreign language in any country you have to speak the native language.
The "best" countries is literally as vague as your personal preference of the entire globe. Do you like borsch, varenyky, vodka, and Russian women? Well my good sir, Russia just may be the place for you. Do you like Peking duck, Baijiu, and Asian women? Maybe give China a shot.
As far as the easiest, you don't "have" to have a degree or even tefl/celta to teach English in China, Russia, some countries in South America, and few other various countries I'm sure I'm forgetting. If you do have a degree then the world is pretty well your oyster but parts of China, South Korea, Japan, and the Middle East tend to pay the best along with other benefits. Obviously any experience, relative degrees, and teaching certificates will give you the upper hand.