You’re in luck: a language purpose-built for a potential world government has already been invented: Esperanto. (bit.ly/guardian-esperanto) The trouble is, not many people speak it. Another solution might be to examine regions of the world with single governments and a lot of languages. In India, there are 17 official languages; these are languages into which all government documents & forms must be translated. In the EU, where legal & trade agreements proliferate, there are 24 official languages. Hm. Seems inefficient, but then again, it also seems to work. For an interesting article on the efficiency or inefficiency of various languages, see this one from The Atlantic: bit.ly/efficient-language.