Load a set of fonts in the fontmap that can be used to render a font matching desc.
| this |
a `PangoFontMap` |
| context |
the `PangoContext` the font will be used with |
| desc |
a `PangoFontDescription` describing the font to load |
| language |
a `PangoLanguage` the fonts will be used for |
|
the newly allocated `PangoFontset` loaded, or null if no font matched. |