I was looking at the descr_sound_strat_* files recently and there's nothing there that lets you modify which sounds go to which culture. The only fix I can think of would be one of 3 things:

1. Make completely new sounds (I don't see this happening any time soon, with the number of people able and willing to do voice acting for RTW). This would get the best result, though.

2. Unpack the sounds, rename them, and pack them back (this way, Greeks could say "Imperator" and have speeches about the glory of Rome instead of Seleucids). You're just moving the problem around.

3. Maybe BI or the 1.5 patch have better options for cultures here. But from what I've read, the voices are off in those games, too.

Basically, I see no solution to this issue with the next patch or any patch in the future, unless it's #1.