Unfortunately, several people have had issues with this. The developers did look into it, but could not find any reason for it not to work, and suspect this might somehow be a windows issue. But I don’t think anyone checked the size of the plugin before, perhaps that is indeed important somehow.
Some people experiencing this issue were able to get around it by running the game as admin and in compatibility mode. If you have the game unpacked somewhere else at the moment, it might also help if you moved it to Program Files (x86) and then gave it the appropriate permissions.
You can check if your SAPI works fine otherwise by pressing windows+r, pasting in c:\windows\system32\control.exe then navigating with tab and enter to Ease of Access, Speech Recognition, Text to Speech. But it’s probably going to work there just fine.
Since you bought the game on here, you now have a DRM-free copy that you can take with you anywhere. So if nothing can be figured out, I hope you can manage to borrow someone’s computer. I’m sorry for the inconvenience. :(