I don't understand why, but StandardFonts class>>#setFontsFromSpec: does not seem to work with the new fonts using a spec generated by StandardFonts class>>#getCurrentFontsSpec, while the following code does work for me:

"From Pavel"

SourceCodeProRegular new install.
OpenSansRegular new install.
FreeTypeFontProvider current updateFromSystem.

"Set some specific fonts and sizes"

#(
�� �� �� �� #(#defaultFont: 'Open Sans' 12)
�� �� �� �� #(#listFont: 'Open Sans' 12)
�� �� �� �� #(#menuFont: 'Open Sans' 12)
�� �� �� �� #(#windowTitleFont: 'Open Sans' 12)
�� �� �� �� #(#balloonFont: 'Open Sans' 10)
�� �� �� �� #(#codeFont: 'Source Code Pro' 11)
�� �� �� �� #(#buttonFont: 'Open Sans' 12)
�� �� �� �� #(#haloFont: 'Open Sans' 10)) do: [ :spec |
�� �� �� �� �� �� �� �� | font |
�� �� �� �� �� �� �� �� font := LogicalFont familyName: spec second pointSize: spec third.
�� �� �� �� �� �� �� �� StandardFonts perform: spec first with: font ]

I like the window title font bold, but I didn't manage that ;-)
Anyway, this might be useful, I seem to remember Esteban had some trouble there as well.

Sven