Despite the human rights principle of no discrimination, the growing numbers of imprisoned linguistic minorities around the world face multiple inequalities related to communication barriers: from cultural and social isolation to lack of equal access to facilities and services. This international survey of prison language policies shows that, in general terms, the protection of prisoners’ language rights responds to non-binding international provisions and scarce broadly-defined national ones. At the individual level, however, prison systems can be grouped according to two distinctive factors: (a) the comprehensiveness of their prison language policies, and (b) the type of policy instruments used to provide for language issues. This article describes the content and extent of language, translation and interpreting policies in forty prison systems around the world, placing a final focus on California and England and Wales, which emerge as examples of good practice that could potentially inspire other systems.