Here is a report on the German forum:
http://simutrans-forum.de/forum/index.php?page=Thread&postID=112540#post112540
Since the update on Feb 13th, simutrans cannot be started.
It appears the Steam OSX install has a corrupt SDL2.framework that it auto installs to ~/Library/Frameworks. Lots of files missing...
However, I'm unable to duplicate the error. I've tried completely removing SDL2 ( I normally have it in /Library/Frameworks for system wide use rather than per user), and Simutrans does still launch with only the seemingly corrupt version it installs. Maybe this user has a 'super corrupt' framework somehow?
He resolved this problem by downloading SDL2 (again?) and copying the SDL2.framework into the simutrans directory.