This project have me hyped!
I own the original 6CD MS-DOS version, which included Spanish subtitles and GUI, which GoG and Origin releases are lacking.
I was working long time ago with the OP of this thread: https://www.wcnews.com/chatzone/threads/russian-translation-of-wc4.27188/page-2#post-410884 trying to extract the spanish files of the disks, but the OP vanished.
If you are considering new language additions, I'd like to help.
Absolutely; and if you want to make a patch like the Russian one so it works on the original too I can give you pointers (although not too much time). With the wctoolbox it'd be even easier now.