What will be the most important language to know in the future?

I really want to learn a second language to help with my future career. I hope to work for MI6/5 or in international relations.
I already speak fluent english, so what language will most impress a prospective employer and help most with my future career?
Thanks all answers are really appreciated.
Please give a reason for your answer.

What is a VPN?

VPN is (Virtual Private Network) were first used by companies to enable their employees to securely access internal systems such as email remotely (e.g. from home or while on business trips). Today they are increasingly being used for personal use by individuals to protect their privacy while online in public places (e.g. when using the wi-fi connection in a cafe) or in a country where the internet is censored / blocked (e.g. China, Saudi Arabia…).