*** a/src/bin/psql/tab-complete.c
--- b/src/bin/psql/tab-complete.c
***************
*** 408,413 **** static const SchemaQuery Query_for_list_of_views = {
--- 408,419 ----
  " WHERE lanname != 'internal' "\
  "   AND substring(pg_catalog.quote_ident(lanname),1,%d)='%s' "
  
+ #define Query_for_list_of_languages_inline \
+ "SELECT pg_catalog.quote_ident(lanname) "\
+ "  FROM pg_language "\
+ " WHERE lanname != 'internal' "\
+ "   AND laninline != 0"
+ 
  #define Query_for_list_of_schemas \
  "SELECT pg_catalog.quote_ident(nspname) FROM pg_catalog.pg_namespace "\
  " WHERE substring(pg_catalog.quote_ident(nspname),1,%d)='%s'"
***************
*** 618,624 **** psql_completion(char *text, int start, int end)
  	static const char *const sql_commands[] = {
  		"ABORT", "ALTER", "ANALYZE", "BEGIN", "CHECKPOINT", "CLOSE", "CLUSTER",
  		"COMMENT", "COMMIT", "COPY", "CREATE", "DEALLOCATE", "DECLARE",
! 		"DELETE FROM", "DISCARD", "DROP", "END", "EXECUTE", "EXPLAIN", "FETCH",
  		"GRANT", "INSERT", "LISTEN", "LOAD", "LOCK", "MOVE", "NOTIFY", "PREPARE",
  		"REASSIGN", "REINDEX", "RELEASE", "RESET", "REVOKE", "ROLLBACK",
  		"SAVEPOINT", "SELECT", "SET", "SHOW", "START", "TABLE", "TRUNCATE", "UNLISTEN",
--- 624,630 ----
  	static const char *const sql_commands[] = {
  		"ABORT", "ALTER", "ANALYZE", "BEGIN", "CHECKPOINT", "CLOSE", "CLUSTER",
  		"COMMENT", "COMMIT", "COPY", "CREATE", "DEALLOCATE", "DECLARE",
! 		"DELETE FROM", "DISCARD", "DO", "DROP", "END", "EXECUTE", "EXPLAIN", "FETCH",
  		"GRANT", "INSERT", "LISTEN", "LOAD", "LOCK", "MOVE", "NOTIFY", "PREPARE",
  		"REASSIGN", "REINDEX", "RELEASE", "RESET", "REVOKE", "ROLLBACK",
  		"SAVEPOINT", "SELECT", "SET", "SHOW", "START", "TABLE", "TRUNCATE", "UNLISTEN",
***************
*** 1543,1548 **** psql_completion(char *text, int start, int end)
--- 1549,1572 ----
  		COMPLETE_WITH_LIST(list_DISCARD);
  	}
  
+ /* DO */
+ 	/*
+ 	 * Complete DO with LANGUAGE.
+ 	 */
+ 	else if (pg_strcasecmp(prev_wd, "DO") == 0)
+ 	{
+ 		static const char *const list_DO[] =
+ 		{"LANGUAGE", NULL};
+ 
+ 		COMPLETE_WITH_LIST(list_DO);
+ 	}
+ 	/*
+ 	 * Complete DO LANGUAGE with in-line-able languages.
+ 	 */
+ 	else if (pg_strcasecmp(prev2_wd, "DO") == 0 &&
+ 			 pg_strcasecmp(prev_wd, "LANGUAGE") == 0)
+ 		COMPLETE_WITH_QUERY(Query_for_list_of_languages_inline);
+ 
  /* DROP (when not the previous word) */
  	/* DROP AGGREGATE */
  	else if (pg_strcasecmp(prev3_wd, "DROP") == 0 &&