Just correcting the other definition for this phrase, "bai bai" is NOT Japanese for "bye bye". If you have to put it as an Asian language, it's Chinese for "bye bye". When you say "bye bye", in Chinese it sounds like words that have Chinese pinyin (the system that helps you to read Chinese words) for "bai bai".
And Japanese for "bye" is sayonara.
It's widely used among Chinese kids.
"g2g, bai bai~"
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