As the most important factor to start and keep learning is motivation, it's maybe better to focus on this starting point...
Need: I want to visit China, I am an export manager...
Passion: I love Korean dramas, fond of egyptology, bier lover,...
Opportunity: living at the border, a Chinese neighbour, a Russian girlfriend/boyfriend
Stress coefficient: Italian is easy (I am a Romance language native), Bulgarian (knowledge of Russian), ...
"Officials" Languages of the worlds: United Nations pack
The most spoken factor: Mandarin, Hindi...
My choices:
German, Italian, Spanish, English for business (and travels)
Chinese: my Taichi teacher is a native and use Chinese and my new neighbour is Chinese
Russian & Ukrainian: long time friends. So happy I am learning their language!
Sometimes:
Korean: Viki alcoholic
Hindi: just curious and the voice India with incredible singers...