People developing applications use glib and use gint,gchar instead of (int, char) for most of times.
But they are not highlighted .So the code looks not that much awesome. The same problem goes for any external library or user defined datatypes. To make the code look more better, gtksourceview should support adding keywords dynamically.

   Idea :- adding api functions to gtksourceview such as add_keyword, remove_keyword,enable_dynamic_keywords,
disable_dynamic_keywords, load_keywords_from_file (returns a unique key which should be used to disable those
keywords latter),disable_keywords_with_key and few others. 
  The processing of symbols should be taken care by external tools  or IDE using gtksourceview.