@ParadeGrotesque
I agree with this article:
"no one really knows what it means at all."
Yipee is fairly common in English, although perhaps a little dated these days. I understand it as an expression of excitement or joy.
Ki-Yay, on the other hand, is meaningless, to me. I think they are non-lexical vocables introduced by, as stated in the article, by Bing Crosby.
https://faroutmagazine.co.uk/yippee-ki-yay-origins-of-die-hard-iconic-phrase/