Non-governmental development organizations (NGDOs) are responsible for ensuring basic human rights for socially marginalised people. In situations of migration, people's opportunity to regularise their migratory status and to secure their fundamental rights to key public services is entirely dependent on communication with the local administration. To support these processes for those who are not fluent in the language(s) of the destination country, NGDO workers must learn how to provide effective interpreter-mediated communication services. In 2019-20, the "Linguistic mediation for development cooperation" (MELINCO) project brought together a multidisciplinary team to explore and respond to the communication needs of third sector organisations serving migrant populations. It included a self-study project involving the development and delivery of a training for NGDO staff, which was aimed at helping them select, prepare, and work with interpreters. The training was delivered online and was based on a needs assessment that involved data collection with NGDO representatives and interpreters. It received highly positive evaluations by participants in terms of course design, contents, and methodology, but our analysis also yielded directions for improvement in terms of extending opportunities for debate, design of practical applications, as well as facilitating participation in virtual learning environments.