Two linguists visit Siberia, India, Bolivia, and Arizona to find native speakers of dying languages. In doing so, they address some of the reasons languages become extinct: no writing system, colonization, economic opportunities associated with speaking a dominant language, social pressure to stop speaking a language.
But the most compelling reason to try and document dying languages: that language is the complex expression of human knowledge itself, and unique ways of seeing the world will die with the language's last speaker. In India, for instance, they found a numerical system based in both 12 and 20; in Bolivia, a moribund language taught to only male healers contains generations of medicinal knowledge; in Siberia, one-word sentences include subjects, verbs, and objects.
For me, the most powerful takeaway from the film was something one of the linguists said, in a call to action for fellow linguists: "I don't see how you can justify devoting your research career to the syntax of French - a language with millions of speakers - when the skills that you possess could help document a language that is going to go extinct in your lifetime."
I know not everyone (in any field) feels called to be an activist, and that linguists who do study the syntax of dominant languages are also doing good work and contributing to the body of human knowledge. But that statement was one of the many poignant moments from the film. Another would be the last speaker of a vanishing language in Arizona admitting that he talks to himself in it because there's no one left with whom he can carry on a fluent conversation.
Again, I'm admittedly biased because my own mother didn't teach me or my sisters Tagalog (and we resisted the few lessons she sent us to anyway - children choosing not to speak languages is another reason they die). Tagalog is by no means a vanishing language, but passing on a language to children can be incredibly difficult if it's not spoken in the home or elsewhere in their lives. Mi Hermana is having problems teaching the pingüinitos Spanish while living in Michigan, and La Otra Hermana is trying to teach the kiddos Samoan completely separate from any regularly spoken exposure to it.
Since St. Patrick's Day is just around the corner and all things Irish are everywhere in America, I'm reminded of some of the classes I took comparing the Welsh and Irish efforts at reviving the respective languages that English eventually replaced. Some were successful, some were not; elsewhere in the world, resources are not necessarily available to resurrect a linguistic identity and culture.
At any rate, The Linguists is definitely on my list of highly recommended films.