I would pick :1. Spanish (3rd most common language, just under Chinese and English and useful in Europe and North & South America)
2. French (Useful in Europe, beautiful pronounciation)
3. German (Useful in Europe, Germany - strongest in economics among Europe countries)
Would not pick :
1. Korean - only useful in Korea
2. Japanese - only useful in Japan and Japan is going to disappear in the world
There is not many people who can speak spanish in HK. But if you step out of HK, there are lots of people who can speak spanish. Even if you go to L.A./San Diego, CA or south part of USA. There are lots of hispanic.