Provides access to [class@Language]s.
`GtkSourceLanguageManager` is an object which processes language description files and creates and stores [class@Language] objects, and provides API to access them.
Use [func@LanguageManager.get_default] to retrieve the default instance of `GtkSourceLanguageManager`, and [ method@LanguageManager.guess_language] to get a [class@Language] for given file name and content type.