Now that I’ve finished the game, i see on the box “with the original character voices”…
OK… but I’ve never heard voices in this game and I don’t find any options to switch it on… 
Did I forget to do something ?
Kana Little Sister doesn’t have voice acting. The information on the box is incorrect.
OK Thank you.
I’m kind of relieved and… sad in the same time :D.
There’s a remake called Kana Okaeri, which has never been translated into English. It has full voice acting (except for Taka).
http://www.cd-bros.co.jp/takayashiki/soft/kana/
Kana Okaeri follows exactly the same script as Kana Little Sister, but the graphics have all been redrawn, with completely different character designs. The music is the same as KLS, except for a couple of additional vocal songs.
^ That reminds me, why did PP/JAST localize the original instead of doing Okaeri?
G-Collections released the translated version of Kana Little Sister in 2002. Kana Okaeri wasn’t released in Japan until a few years after that.