Looks like a reasonable addition by inspection (can't build _anything_ on this Windows tablet ;-).
:(
The tooltip looks fine, but as noted the menu label looks a little long, its 5 longer than "Toggle all additional widgets" the current longest in the menu. Maybe simply "Show different line endings".
I guess you are talking about the View menu? There is no menu item, only a checkbox in the preferences dialog: 
The idea is that users probably will not change that setting so often but rather decide once to show all line endings or only differing ones and therefore I did *not* add a new menu item to the View menu.
I just re-pushed to not accidentally remove trailing whitespaces in geany.txt.