The "Language Files" option of the Windows' installer only disables language files for Geany, but not for Gtk runtime. As a result, the installation takes 68.7 MB, 33.5 MB (49%) of which are MO files of Gtk in "share/locale" folder. However, the real issue is not the disk space but the fact that the interface becomes partially translated.
The same problem is with the installer for plugins.