i think the "best language" is a subjective point of view,it depends on the purpose of your learning. for example spanish is one of the most widely spoken languages in the world and it would be useful learning it ...and italian is a beauuuuuuutiful language! =)

russian or spanish if you want something difficult than it's russian, if easy than it's spanish they are both widespread and beautiful (IMHO) I like Spanish singers very much. if you like history, or astronomy you could choose Greek

If you are in business/politics I would suggest English/Mandarin/Russian as the three languages to speak. If you want a bit of a fun challenge you could try Latin - credo quia absurdum est! Hahaha.

tibetan

norwegian