Create a script called Terminal (yes, without a extension) inside the folder ~/.local/share/nautilus/scripts with the following content:
#!/bin/sh
gnome-terminal
Make it executable, then close any Nautilus instance:
$ chmod +x Terminal
$ nautilus -q
Create (or edit) the ~/.config/nautilus/scripts-accels file adding these lines:
F12 Terminal ; Commented lines must have a space after the semicolon ; Examples of other key combinations: ; F12 Terminal ; F12 Terminal ; F12 Terminal