In science and in all other domains that require communication across borders, we need one lingua franca, and this lingua franca will be English. The adoption of the native language of some as everyone's lingua franca unavoidably raises a problem of justice in various senses. One of these is cooperative justice, the fair distribution of the cost of producing a public good. This article proposes a criterion of fair burden sharing--proportionality of cost to benefit--and explores its policy implications. Does this criterion require a linguistic tax on the native speakers of the lingua franca in order to subsidize the learning of it by all others? If so, how high should the subsidy be, and should it be pitched at the same per capita level for all learning communities? If not, is there an alternative way of implementing a fair compensation for the free riding of lingua franca natives on everyone else's learning? Among the article's conclusions are that fair subsidies would need to be directed disproportionately to the Chinese--even abstracting from possible differences in the difficulty of learning English--and that more hopes should be focused on the compensatory poaching of the web than on anything resembling a linguistic tax.