Hi guys. I have good news.
I found how to add a language to Windows Home Premium.
Everything is here and in English.
First you will go on that site to download the LANGUAGE PACK that you want. In my case it was the French one.
Once you have it, go on this site and fallow the directions:
Note that during the step 6, you might get a message saying that you need extra Microsoft addons. Don't panic! The program will offer them to you. All you will need is to click on the missing addons, downloading and installing them and that's it. You will be able to change your language. The program will ask you to reboot your machine. Once Windows is rebooted you will see your new language. And YES you will see the new voice recognition language pack. And you will see that language pack added in Voice Attack.
For any question concerning that topic, do not hesitate to contact me.