You have posed an interesting question! My favorite word is, OK-dokey, which means OK, agreed, let's do it. OK, according to some sources, is the most commonly used word in the world. My English language students, either on or offline, in Thailand, South Korea, Malaysia and Latin America often use the "OK".
For example, take the two people above, husband and wife. They live in a jungle rainforest. The husband says to his wife, "Honey, how you feeling today?" She says, "OK, how are you?" He says, "Still in love with you, forever, and forever, OK!"