The game lacks subtitles in the cgi cutscenes, except in french.
Some fans translated those and embeded then on the videos- all needed is to download and replace the files

1) Download the video files:
https://www.dropbox.com/s/djvrdj0aac04zxx/movies.7z?dl=0
copy the files

2) go to this folder under the games directory: "steam\SteamApps\common\The Book of Unwritten Tales\kagedata\lang\data\movies" and paste/replace.

Now the substitles will apear on the videos in-game.

Thanks to the users Zund, Snicker and Mdqp who figured it all out
Original discussion: https://gtm.steamproxy.vip/app/215160/discussions/0/882965737363269396/?ctp=1