I have finally shipped a full working example for use of GTK3 menubar with GAction and GMenu.
Starting a few days ago on a first draft of C. Eric Cashon (Windows system menu doesn't work)
I have added examples for statefull actions, toggle- and radio-buttons and Keyboard shortcuts.
This is currently only the menubar variant, gears menu examples may follow eventually – I guess they are not too different.
Well this example is for Nim language, but code layout is of course very similar for many languages – C code generally has the same basic shape but more boilerplate.