The games are made with
AGS which supports multiple languages. To translate a game to spanish, you'd need the english translation, as all MMM games' default language is german.
Simply ask one of the authors of the already translated episodes for the english translation file.
Open this file with a text editor, replace every english line with its spanish equivalent and send it back.
Btw, AGS is made by a british guy called Chris Jones, so you should be able to make your own MMM game by using the template on the
MMM website.
You'll need a good unterstanding of AGS, though. The scripts in the template are quite well documented, but the only tutorial for understanding its special mechanics has not been translated yet.