Yuna actually gives a very different impression in the Japanese version of FF10;
her voice is more high-pitched in that version, she has a very girly giggle, she sounds a lot younger, and she speaks with a bit more power.

For example, her line "I've done it - I have become a summoner" sounds rather worn out in the American version, but in the Japanese version she states this with a kind of confident and energetic "yes! I've done it!" ring to it.
She doesn't actually say it in that way - her Japanese line in that scene is identical to her American line - but it feels a lot more like that.