When will Apple Pay be launched in South Korea?

Get more help and assistant from Apple directly, see Contact Apple for support and service -> Contact Apple for support and service – Apple Support (UK) 

We don’t know, we are also users of Apple products & services like you.

Whenever South Korean Banks, card issuers and merchants support it.

Apple can help them implement the feature, but the banks and stores need to want to support it. Apple has no way of firing that on them.