As a side-note, even though OK is also used in Japan this paragraph interested me:
“Almost every language has an O vowel, a K consonant, and an A vowel. So OK is a very distinctive combination of very familiar elements. And that’s one reason it’s so successful. OK stands apart.”
In Japanese there actually is not a long A vowel. OK is usually written オーケー which phonetically is oh keh with elongated vowels.