Comment # 33 on bug 951898 from Frederic Crozat

(In reply to Dominique Leuenberger from comment #32)
> (In reply to Frederic Crozat from comment #31)

> > I tested it for a week, it worked fine. However, we'll need to update some
> > GNOME branding too, since Cantarell is specified by name for windows titles.
> 
> Indeed, preferably we set it also to the family, though - not to the
> explicit name.
> 
> Which one should it be for
> org.gnome.desktop.interface/titlebar-font ?

I double-checked on Leap and we have two settings :
[org.gnome.desktop.wm.preferences]
# titlebar-uses-system-font = false
# titlebar-font = ""

So, it looks like just changing the system font is enough (I was tricked by
GNOME Tweak tool which doesn't follow titlebar-uses-system-font value),
upstream has titlebar-uses-system-font=true

So, Sans 11 should be enough..