added callback in C for unknown words

src/runtime/c/utils/pgf-translate.c

@@ -91,6 +91,8 @@ int main(int argc, char* argv[]) {
 		pgf_new_callbacks_map(from_concr, pool);
 	pgf_callbacks_map_add_literal(from_concr, callbacks,
 	                              "PN", &pgf_nerc_literal_callback);
+	pgf_callbacks_map_add_literal(from_concr, callbacks,
+	                              "Symb", &pgf_unknown_literal_callback);
 
 	// Create an output stream for stdout
 	GuOut* out = gu_file_out(stdout, pool);