Does Riven VR have new recorded voiceovers in English? If not, why aren't the languages that are available in the original Riven on GOG not available in the new Riven VR?

The remake does have new voice over, both to replace some existing dialogue and to add new ones. So, even if it was possible to mod the original localized VO into the remake, some parts would have to switch back to English.

Also, because of the compression needed to fit everything into the CDs, the audio quality was not great, and while Cyan was able to use some of the original uncompressed recordings they had kept (with help from the Video Game History Foundation), it was most certainly not the case for the localized recordings, so the gap between the graphics and audio quality would have been noticeable.

I still think it would be worthwhile to have the old audio sync'd up and available. They could've also run analytics on the Steam version to see which languages are most played, in order to know the popular ones to dub for future games.