Associates a [class@Language] with the buffer.
Note that a [class@Language] affects not only the syntax highlighting, but also the [context classes](./class.Buffer.html#context-classes ). If you want to disable just the syntax highlighting, see [method@Buffer.set_highlight_syntax].
The buffer holds a reference to language.
| this |
a SourceBuffer. |
| language |
a SourceLanguage to set, or null. |