Karthus has no voice clips presently. I was playing with a friend for 5-6 games, he played Karthus each game, and no matter what, he got no voice lines, none on his side, none when he did emotes, none when he ulted. Normal sound effects, like his q exploding played, but no voice lines. 
Yeah, not even on his taunts or anything, on all skins as far as I can tell, I have Pentakill and had no Karthus' lines.
Same issue here, and its really frustrating since im playing karthus a lot these days and sometimes I don't even feel like playing him just because of this issue. I also asked my friend to play a custom game with me, we both picked karthus and started spamming laugh/jokes/taunts but nothing happened. Definitely not an issue on our side, and since Karthus isnt loved by rito, we will just have to wait :/
