So people want 3000 lines of battle chatter, some with important information, in a language they don't understand? You'll probably be detrimental to the team in that case. I'm taking English for my team. Say you're in the Russian army during WW2 and you hear a German guy speaking; you only speak Russian. You now know there's an enemy whereas there's always the chance for mistaking a language if you don't speak it. It's the same idea here except in a language you know.
Anyway, maybe they'll add the option later, but from what they've said it's only going to go based off of localization. Adding all the spoken dialaogue as an option from the start would add a lot more in terms of file size.