Roboto font not working with Openbox GTK3 applications while other fonts do

I am using Debian Stretch with Openbox window manager and I am trying to set the uniform look for GTK2, GTK3, QT4, QT5 widgets. Everything went smoothly except for GTK3 that partially ignores ~/.config/gtk-3.0/settings.ini file which looks like this *(I used Lxappearance to modify it)*: gtk-theme-name=Breeze gtk-icon-theme-name=breeze gtk-font-name=Roboto Medium 10 gtk-cursor-theme-name=breeze_cursors gtk-cursor-theme-size=0 gtk-toolbar-style=GTK_TOOLBAR_BOTH_HORIZ gtk-toolbar-icon-size=GTK_ICON_SIZE_SMALL_TOOLBAR gtk-button-images=0 gtk-menu-images=1 gtk-enable-event-sounds=0 gtk-enable-input-feedback-sounds=0 gtk-xft-antialias=1 gtk-xft-hinting=1 gtk-xft-hintstyle=hintfull gtk-xft-rgba=rgb Option gtk-font-name=Roboto Medium 10 is completely ignored by all GTK3 applications which continue to use their default font Sans 10 while option gtk-font-name=Monospace 10 works. Other options like gtk-button-images=0 also work if I change them and restart GTK3 applications. So what can I do to be able to use Roboto font in GTK3 applications inside my Openbox window manager? Roboto font works for GTK2 applications in ~/.gtkrc-2.0. It looks like gtk-font-name="Roboto Medium 10" *(mind the quotes which should be avoided in GTK3 configuration file)*. Roboto font also works for QT4 and QT5 applications and was applied using qt5ct... So only GTK3 is making problems for Roboto fonts...