OK, I finally got my own solution, thanks to this post
To anyone interested :
- Install the GOG version.
- Download this archive
- Replace dialog.tlk and dialogf.tlk in the game with those included in the archive.
This solution is better than ERISS' one, because you don't ever modify any binary file. You can even use this solution on the Linux client, if you install it reading the instructions from Bioware
I assume that this should work with other languages too, if you can find their updated .tlk files anywhere on the Internet.
Problem solved :)