Diamond is a Professor of Geography at UCLA. In this book he discusses his studies of less developed societies and their transformations. He has made many trips to New Guinea and uses what he has learned there for many examples.
When he talks about languages he says that there are ~7,000 distinct languages in the world but that many of them are becoming extinct due to the influence of the modern world. In New Guinea each small set of people residing in a section has its own language. Neighboring communities have different languages - he stresses that these are not dialects and most people also speak the several languages of neighbors. Once at a campfire he asked every to say ho many languages they speak. Most people said that they could speak at least 5 languages and one person said it was 15 for him. Diamond is a bird watcher so he has had to learn the name of many birds in many languages to that when fellow locals point out a bird he knows what they are saying.
He has a interesting section about diseases. Of course in some of these native populations with no medical care people die of things that would be easily cured in the western world. On the on the other hand in a small closed society when a communicable disease spreads around the peole who are survive have probably developed immunity so the disease doesn't strike again for many years. But then he writes at length about epidemics of non-communical diseases (NCDs) which are so prevalent in the western world: diabetes, heart disease, strokes, etc. The principal cause of these is diet, environmental factors, and lack of exercise - genetics too of course. In these more primitive societies there is no sugar or salt added to anything - people's salt intake is often 1% of a typical western person. Everybody walks a lot, carries loads, doesn't eat fast food or all the sugar and salt added stuff that we find at the supermarket, and doesn't sit around watching TV or playing video games. It used to be that he saw no obese or even overweight people in New Guinea. Now in the big cities there are some because of the western influence. He gives several other examples - the Pima indians in the US who now are very overweight; about ~70% in the 55-64 age range have diabetes. He emphasizes that these NCDs are really epidemics because social pressures, the processed food chain, and pollution related effects cause the spread.
He describes a social scientist label for our type of society as WEIRD for western, educated, industrialized, rich, and democratic. Interesting thought.
I definitely recommend the reading of his books. They are heavy going but very thought provoking.