Ok, I've checked some things, and finally I'm thinking on leave SUBS+VOICES for in-flight comms in WC Privateer. They are not perfect, but are very intuitive. The last message normally lasts 1-2 seconds in disappear, but I think the result is pretty good.
For in-game dialogues I used the texton thing. It works very well. And for intro cinematics I have done the voices with text-to-speech with spanish speaker, and they are good (but not professional :( ). So, I have now all the game with voices + subs or spanish voices. Maybe the intro can be modified also to present voices+subs, but I don't want to check this, there are only a few voices and they can be done easily.