Here is the trick:
A Russian tourist riding a moped or small scooter gets stopped by police. He has a drivers licence but no international drivers licence. He pays 500 baht and is allowed to continue driving around despite breaking the law.
Our Russian friend gets tired of constantly sponsoring the police with 500 baht when he is out on a trip so on his next visit to the tourist destination he brings along an international drivers licence, thinking he is safe from the money collectors.
– Naturally he gets stopped once again, fined another 500 baht
– But I have an international drivers licence, he argues
– This is a drivers licence for a car, not a motorcycle, says the policeman
– But I am not driving a motorcycle, I am driving a moped or a small scooter. A car drivers license is sufficient.
– No motorcycle licence, you pay 500 baht, says the policeman
And our Russian friend sees no point in continuing arguing. He is left no choice but to pay 500 baht.
In most countries a motorcycle with a large engine requires a motorcycle licence. Practically no tourists have such a licence. Generally a scooter or a moped do not require a motorcycle licence.
From a practical point of view, in most countries mopeds or small scooters can be ridden without requiring a motorcycle license. A car license is sufficient.
International drivers licence or not, it does NOT make any difference when you are visiting a certain city in a certain country.
This has nothing to do with enforcing the law. This is about something entirely different.