"Ding-head" is not a common English slang word. However, I think that many speakers of English would understand it, because it's similar to other "ding" words -- dingaling, dingbat, dingleberry. All of these words, including "ding-head," indicate someone who is stupid or out of his mind. (See the pages in Cassell's Dictionary of Slang for
"ding" words.)