How to create custom keyboard shortcuts in Thunar File Manager

$ cd ~/.config/Thunar

Open uca.xml and accels.scm.

In uca.xml, copy the <unique-id> value (a numeric string) for the custom action (e.g. "Open Terminal Here") you want to target.

Search for it in accels.scm. You will find it in a line of this form:

; (gtk_accel_path "<Actions>/ThunarActions/uca-action-1552605449573546-1" "")

Check your preferred custom keyboard shortcut in Thunar to ensure it currently has no effect.

Then add it inside the second pair of quotes and remove the ; at the start so as to uncomment the line, giving, for example

(gtk_accel_path "<Actions>/ThunarActions/uca-action-1552605449573546-1" "<Alt>t").

Save the file, log out and in, and it should work.

Notes:

<Alt>, <Shift> are self-explanatory, <Primary> means the Control key. Function keys are typed as F1, F2 etc. Just append the target key to the modifier, so <Primary>x, <Alt>p etc..