Just been to Korea last yr.
Subway very good and easy to understand.

No worry. Staff at the subway more than happy to help.
Most shops at major shopping areas have staff which do speak in Mandarin.
Taxi very expensive and one way to city which took 20 mins drive cost me close to RM200.

I fly by MAS and EVA air to Taiwan both around RM700+ inclusive of tax.
So we let u decide.
Dec and Jan weather should be cold and not much of shopping that u can do cause they are selling winter clothing.
If u wan to buy clothes then u shud be there by Sept or Oct.

BLOODY SICK OF TRYING TO BOOK MY FLIGHT THROUGH AA!
HOW THE HELL DID U ALL ABLE TO BOOK THE TICKET?