I see I'm not the only one who have this problem...
I've contacting STEAM's Support and 1C's Support, but no response yet.
Because I really don't like empty space, and because I really enjoy with Starwolves's english voices, here is a compil of SW1 and SW2 english voices specially done for SW3.
It makes 30Mo and you have to unzip
this in your SW voice folder.
For me for example:
C:\Program Files\Steam\SteamApps\common\star wolves 3 civil war\Data\LocData\English\Voice
Hope this help
Cordially