Well in English Laharl is voiced by the woman who did Rita Repulsa from Power Rangers. He's supposed to sound like a brat though.

Honestly, if it bothers you I say go for the Japanese voices, it's a good voice track. And Gordon, in either version, is just spot-on. Flonne is happy and bubbly in either version because that's how she should be, Etna's English is slinkier and sultrier whereas her Japanese is more chipper.