Legal Question in DUI Law in California

You can hire an attorney, who can appear on your behalf (as long as the DUI is charged as a misdemeanor -- meaning nobody was injured or killed, and you didn't have three or more qualifying prior DUI convictions within ten years).

Because you are a nonresident, it is unlikely you will be ordered to serve jail time unless you have prior convictions or you injured someone.

You're right... there is no way to enforce any sort of penalty for this conviction, and you certainly will not be extradited from Australia to face DUI charges. However, failure to handle this matter is very likely to cause problems if you ever try to return to the USA.

In some jurisdictions, the District Attorney may even agree to dismiss the charges if you do not plan to return to the United States. (That doesn't mean you might not make travel plans in the future...)

Depending on additional facts, this should not be any problem.

If you are not returning to the US, it is not a problem.

If you are returning to the, we or another attorney can handle it for you. Jail should not be a concern at all

You can hire an attorney to represent you in court here. He can negotiate a 'plea bargain' for you . As long as there is no jail time imposed, you will make it through the process without having to come to the US. Given the circumstances, with no 'priors' on your record, the most likely outcome is fines. You should not ignore this and thereby have an arrest warrant issued. That would be entered into the DOJ database, and would prevent you from re-entering the country, and might affect you in AU. If this occurred in Southern California, feel free to contact me for the help you need.