Learning another language is not a haphazard activity. You need to have some reasons for choosing which languages you want to eventually speak. Here are my criteria:
1. Number of Speakers
The number of speakers is not a major consideration for me, unless I am in it for the money, in which case, the more speakers a language has, the larger the market would be and more opportunity for profit. I don’t discount the number of speakers though, in that a language has to have minimum number of speakers large enough for variety and possible social encounter in one’s lifetime. Realistically, I don’t intend to talk to each and individual person speaking a particular language, but only a select few that I find interesting or share similar interests with. I don’t even have to talk to people, I just might want to enjoy their creative output, like listening to their music, speeches, radios, or reading their writings, or watching movies or TV shows. In other words, the language just has to have sizeable creative output I am aware of or was made aware of that interests me. In terms of speakers, any language with 1 million speakers or more already ticks my criteria for number of speakers. If I live for 75 years and I have 50 years free to interact with each and every person in a 1 million-speaker language, that would mean 20,000 a year or 55 person a day. So, 1 million speakers is just the threshold for me.
My target language has to have a distinctive culture (food, technology, music, literature, other arts, science, religion, philosophy) the spirit of which can only be transmitted through that language. I think all languages are culture specific, in that the things valued in that culture are reflected in its vocabulary and grammar. So, being able to describe this culture in another language is not enough for me, its not the same as physically smelling, touching, seeing, hearing and feeling under that language.