What version of GTK, installed how on what kind of system? Where exactly is the directory located? And the inevitable question: Why do you feel you need/want to delete stuff that it has presumably preinstalled for a reason?
I was thinking first at Gtk 2.24.20. However I have two, 3.4.0 and 2.24.20.
The first is located at: /media/34GB/Arquivos-de-programas/Gtk±3.4.0/share.
The second is at: /media/34GB/Arquivos-de-programas/Gtk+2.24.20/share.
For the most noble reason of all: To save disk space. I will probably also delete the gtk-doc dirs, though I intend to keep them in my compressed gtk’s backup dirs.
It should be fine. However, if you are using a package manager for the files in those directories, there may be a better way. Some distros have documentation and translations in separate packages. You could uninstall those specific packages instead.