Good question. Language is indeed part of the development communication discourse. From the seventies onwards, devcom majors study Hymes (language), Birdwhistle (kinesics), Hall (proxemics) and Randall (nonverbal communication) as part of their communication and culture courses. However, indigenous language has hardly been part of this conversation. My sense is that devcom should encourage the blossoming, (i.e., development) of indigenous languages but, at the same time, encourage a national language and eventually, a lingua franca - Espanol, Francais or English in former colonies of Spain, France or Britain - specifically for communication purposes. Indeed, development communication materials using indigenous language, music and other art forms are essential. But this should be supplemented by developing literacy in the national language and eventually in a lingua franca.

Indigenous languages or dialects (for this matter) should be the major forms of communicating development messages to specific audiences considering the English literacy of your targets for example.  Development practitioners and communicators usually include in the project framework or development goals a way of being "culture-sensitive".  Thus, one way is to adapt to the common people's way of talking or speaking (including dialect), their way of expressing themselves as that would be  part of their norms and culture.  Thus, thorough development would be highly affected by how stakeholders or audiences will understand you and your level of commitment will also be gauged by how well are you with their language.  I affirm to the question, a very good one as one just work on indigenous languages but never put into a dialogue before