There is no harmonised legislation or regulations governing the import, purchase, or use of vaping equipment anywhere in the world. Each country has its own rules, but it's possible to classify countries into different categories.
IN EUROPE, most countries operate using similar rules to those for cigarettes : where you can't smoke, you can't vape.
However, you should be wary of countries such as Denmark, where it's illegal to consume e-liquids other than tobacco flavour or menthol.
In Norway, e-cigarettes are regarded as a medical product and are illegal to import, so you'll need a certificate of residence and a prescription before you can buy one.
Some countries, such as Australia and Hong Kong, ban the use of nicotine liquids.
In Japan, you are also banned from buying vape products, so be prepared before you leave.