Yes, it is. Back in the 60's we had sophisticated ratings in Ecuador, and there were a number of research companies that could do perceptual studies. For my news/talk/novelas station, we did some perceptuals in combination with our associated newspaper in the later 1960's
Everywhere I have worked in Latin America from that time forward has had very good research... often better than in the U.S. because labor was so cheap that more interviews could be done within a budget.
Almost every country that has commercial radio has a ratings company and surveys that use the personal interview similar to what The Pulse did. That is a very good system, as properly used aided recall is better than a diary but too expensive to use in the U.S.
Most third world population is now urban, and areas like Sub-Saharan Africa have phone systems tied into an electronic money system where people can be paid, even for piece work, into their phone and buy stuff at the local markets with it.
And, in some areas, the rural zones use vernaculars of very limited usage languages, making it impossible to reach them with wide area short wave.
As an example, Mexico has over 100 languages and dialects, all spoken in limited parts of the country.
Starting with Nahuatl, spoken by 1.6 million Mexicans, there are 16 languages spoken by over 100,000 Mexicans. They won't be listening to Spanish language VOA broadcasts. The same kind of language subsets exist in much of Africa and more rural areas of S.E. Asia.
Beyond that, the education level of rural residents in underdeveloped nations makes any assumption that they might like and enjoy VOA programming a ridiculous assumption.
I'll take your word on the research in third and fourth world areas, obviously you know more about that than I do, having worked in similar areas. Obviously I don't know about how radio is run in those regions, all I can know is what little is available to read about radio in third and fourth world areas. But I would wager that the way media is done in Africa and rural Asia is different than the way it is in Latin America.
I'll admit up front that I could be wrong on that.
As for Africa's cell-based phone banking systems. that undoubtedly works in the cities, but country wide it probably isn't so much the case, because cell coverage isn't as good as it is even in most of Latin America. There are cell coverage maps available for every country in the world, and the African maps in particular show vast swaths where there is no cell coverage. The areas with coverage are in the big cities, and along the main highways. But in the rural areas, where 55% of Africans live, there is very little cell coverage. Internet coverage isn't up to Latin American levels, either, especially as 60% of Africa is in dire poverty.
You're correct about languages, although most African nations have a lot less than 100 languages per country. Usually there are a handful, and a lingua franca, and in schools such lingua francas (French, English, Portuguese, or the native language of the largest majority tribal or ethnic group) are taught along with other subjects. In Zimbabwe, for example, despite the fact that there are 3-4 main native languages (Mashona, Ndebele, and some other dialects) English is taught and understood by the majority of the population. It's the same in Zambia, where the official language is English.
In the former French colonies French is widely spoken and understood.
The main point here being that VOA fulfills a mission, and like many other missions -- whether government or otherwise (religious broadcasting, for example, would be a similar case to what VOA tries to do), the metric is different from that used in commercial media. Either the US government determines that reaching rural Africa and Asia -- where hundreds of millions of people live -- with an American message is important, or it's not. If they think the only way to reach poor people in rural Africa is through an internet device, they might be mistaken. But it's their choice to make.
VOA costs the taxpayer, per year, much less than a $700 million B-21 Bomber or the $37 billion USS Gerald R Ford (and that was 2018 dollars) -- both of which may be already outdated in the day of high tech, drone warfare.