Useful language for Physical Energy?

Hi guys,

I'm considering picking up a new language and I am wondering which would be most useful/relevant for the physical energy world. I understand that English is the corporate language, but I reckon that picking up one more language should prove helpful? (in terms of work and "hire-bility")

I am currently based in Southeast Asia and able to use both English and Mandarin. Should I go for languages like Spanish/French which might be useful for places like Switzerland (albeit more difficult to learn), or a more regional language such as Bahasa Indonesian?

Thanks in advance, any suggestion is much appreciated.

Cheers!