Hello everyone,
Just in case this could help others, I think I finally solved my problems with speech recognitions: using a USB headset.
I had my voice recognition set up and trained as posted in this topic. I even created the exceptions on the antivirus for the files also mentioned here (or in an attached topic at the beginning). However the speech recognition in the game was faulty. I could play (for hours in some cases) but there were many occasions in which the game just couldn't understand me. That meant that everything was working but sometimes it wouldn't get any of my words or it would just make up what I said. Very frustrating.
After checking that everything was set up as it should, I tried using a USB headset (a very very basic one) instead of the jack headset that I was using and... absolute surprise. The game worked perfectly. Not a single problem.
Good luck everyone!