About this question I think we must differenciate between:
1. I chose a language because is a useful language. In this case I think Spanish language has to been study at the school, because it is, after the English, the language more spoken in the world (We must bear in mind Chinese language, of course).
Speak the rest of languages is, also, useful and interesting by several points: Economy, Diplomacy, Science, etc. But, nowadays, Spanish is more useful (speakers number, geographical distribution,...) than others languages.
2. I chose a language because it is useful and just language, but it is not very practical. So I chose Esperanto, because I think all languages hve the same importance. So, for avoid unfair differences, I would chse The Esperanto
To finish: Also I'll allow students chose any languages.