I just can't play with the english voices. They just ruin the mood. Is there any way to disable them?
Yes, you can use this excellent patch by user *ikantspelwurdz*. Follow this forum post:
Yeah, you found it.
The best voice version for AITD1 is in French, but the GOG version has English voices and French text, so it is not worth it. You can download the real French version from abandonware-france for AITD 1 & 2. Alternatively, if you don know French, you can directly play the floppy version. Actually I sort of like the music more. The difference between your approach and the real floppy, is that the floppy version only needs like 11mb.
Aitd3 in GOG has the proper voices, but they screwed up in GOG and they did cut down the first seconds of every dialog, so they miss a couple of phrases every time there is dialog. super annoying. I made a patch for the French version, and there is another one in the forums too for the English version. You overwrite the ogg files form GOG with the patched ones and you'll have proper working sound.