I like the fact that you are focusing on illiterate and multi-lingual populations. They are at risk. Radio, TV and IVR are the best ways to reach them.
IVR systems can be programmed to call people at particular time and can force people to answer phone calls (instead of getting voice mails they would not listen to). The messages could be localized - languages and areas.
Voto Mobile https://www.votomobile.org/ provides a voice platform for notifications and surveys for people in developing markets. They are not established in lots of countries yet (Ghana, Senegal, US).
On the other side, twilio https://www.twilio.com/ (based in the US) works around the world.