For those interested: "jee" is a variation of the exclamation "jes" which is a direct borrowing from the english "yes". However, jes is not used to mean yes, it's an expression of excitement. If you're very excited, add a few more "s" as in "jesss"! Jee can also be elongated: Jeeee!
I would also like to know what yay means in UK English. I looked it up in the dictionary and it stated that it is an informal North American adverb meaning to this extent. Example given I knew him when he was yay big. I am a native English speaker and I have never heard this word used. It also said it could be a variant of yea which is archaic for yes. I obviously can’t comment on the frequency of its use in Finnish but I doubt that the Given English translation of yay adequately conveys the Finnish meaning of jee. For me the supposedly English word yay conveys next to nothing. I think the English translation requires a re-think.