This is something I also want, I've modified
getCountry in speech.lua in DCS World\Sounds\Speech
This is what it looks like, I've only modified one line and you can find the code from this,
just remove the if nativeCockpitLanguage then
and leave return aircraftNativeCountry[message.sender:getUnit():getTypeName()] or base.country.id.USA and you are done