This dissertation explores language policies regarding selection and training of interpreters by the Society of Jesus during 17th and 18th centuries, in the former Paraquaria (the Jesuit Province of Paraguay). The Society of Jesus played a major role in the standardization of indigenous languages, as well as in translation and education policies; all areas of what is now known as language planning. Using as primary sources public and private letters produced by Jesuit authorities during this period, this study identifies overt and covert (Schiffman, 1996) language policies regarding interpreters, their linguistic repertories and the quality of their work. These are considered and analyzed with relation to the political and economic objectives of the Jesuit order and the secular society, in all their contradictions. Research on language policies regarding the interpreters’ agency is considered a direct and productive way of investigating how overt and covert language policies articulate.