Your native languages have an impact on -- and enrichen -- your worldview. The classic examples of this are inuits and amazonian tribes, which use (indeed, need) a few scores of variations of white and green to depict the subtleties of their environments.
It also structures the way you think in some sense, and can yield interesting subtleties in the way you express things and in literature. See how German, for instance, requires the verb to be put to the end of a sentence. With a long enough sentence, you can tickle the imagination prior to reveal what action all the beautiful words were applying to.
Lastly, there's more to it that simply having everyone speak the same language. A language can be very rich in vocabulary, and offer wide variations of vocabulary depending on the individual, and turn into a tower of Babel in its own right. English, in fact, is the best example here. A typical English speaker might know -- or at least commonly use -- something like 20-40k words; someone who speaks international English at a conversational level might typically know and use half of that. Contrast the two figures with the total number of words, which is well north of 500k in total: each specialty field and subculture has its own set of words.
There is good and disturbing work on how language affects decision making (see, or example Lera Boroditsky). In some languages, like, English, you're more likely to say "he dropped the glass and broke it" while in others, like Spanish and Hindi, you're more likely to say "the glass fell and broke", or even "she had the glass and it fell and it broke". So what? Well if you use these formulations in a controlled trial in a single language (e.g. in English: split a group in two and describe a scene to one in an agentive and the other a non-agentive way they end up with completely different views of responsibility, guilt etc). Yes you could in theory do all this work in one language (like Lakoff) but you might not even know that it could be interesting. There are lots of interesting examples.
This kind of stuff can be useful in uncovering (or exploiting) propaganda / advertising, but also decision making in science, law etc. And language is one of our few tools for investigating operating brains since setting breakpoints in brains is frowned upon.
To what degree do these differences really affect culture? Who knows (yet?). I find a full Sapir-Whorf cultural-determinism-from-language very hard to take seriously, but in the small at least it seems pretty likely and who knows how fundamental it is? It needs research.
Plus it's fun. My wife, kid and I use three different languages together even in the house, depending on context or whom we're talking about, or what we want to say or just by whimsy. We listen to different kinds of music depending on mood too. People don't live in a world of fordist Gadgrinds!
And then there are the terms/concepts/ideas particular of a language or their lack thereof. I learnt from a Borges essay, Ancient Germanic Literatures, about the Ulfilas/Wulfila Bible. As I don't have the English translation of this book (and there's no excerpt in Google Books), I'll try to translate Borges (but not his semicolons) myself:
"The Gothic Bible is the oldest monument of the Germanic Languages. Wulfila had to overcome vast difficulties; the Bible more than a book, is a literature; to reproduce that literature, sometimes complex and abstruse, in a warriors and sheperds dialect is a job that would look impossible a priori. Wulfila achieved it with pluck and sometimes with sharp wit. As is natural, he lavished barbarisms and neologisms on it; he had to civilise the language. It holds surprises for the reader. It is written in The Mark Gospel (VIII, 36): "For what shall it profit a man, if he shall gain the whole world, and lose his own soul?" (translator's note: KJV). Wulfila translates world (cosmos, order, in the original) as beautiful house (t/n: fairhvu). Centuries later, Anglo-Saxons would translate world as woruld [wereald, age of Man], that sets human time against the infinite duration of divinity. The concepts of cosmos and world were quite abstract for the simple Germanic peoples."
Efficiency and utility DO matter. We can learn from old or dying languages, sure. Then move on.
I'd extend the argument to species. Whatever curious creatures existed when ecologists came to exist is a coincidence. They are not intrinsically important. We can learn from them. Then move on.
I suppose what I want is to have a more interesting world. If we allow all this interesting data to die before we have the technology to truly capture and reproduce it, it is gone forever. Which in most cases would be ok, I guess, as new things could arise to replace them, right? Newer and better things?
Unfortunately, that can't happen if we never give it space to happen in. We monoculture our world in the name of utility, so the only species that can exist are the limited set we have chosen.
Like data, it's better to store it and maybe use it once or twice, than to need data that doesn't exist at all.
And it's not simply like "a person can speak more than one language". It's actually more than half of the freaking world speaking more than one language. If you happen to live in a region (and I'm not saying "country") where people only speak one single language then it's quite possible you're the exception in fact.
However, I believe there are subtle implied philosophical differences. For example, I perceive German to be more principle-oriented and idealistic in comparison to English, which tends to favor more pragmatic thoughts. As an example, consider the word "Sachzwang", which has no direct English equivalent and roughly translates to "inherent necessity". It is a typical word for a language that thinks in absolute principles. Of course, it is also possible to express this in English, it is just a little less convenient and thus also less frequently done.
It's like different programming languages that are all turing-complete, but some allow to express certain things more effectively. From that point of view, having fewer languages would also come with a reduction in diversity of thoughts.
"Indeed the people are one and they all have one language, and this is what they begin to do; now nothing that they propose to do will be withheld from them.
"Come, let Us go down and there confuse their language, that they may not understand one another’s speech.
"So the Lord scattered them abroad from there over the face of all the earth, and they ceased building the city.
"Therefore its name is called Babel, because there the Lord confused the language of all the earth; and from there the Lord scattered them abroad over the face of all the earth."
https://en.wikipedia.org/wiki/Tower_of_Babel
The lesson is that language diversity prevents coordinated work.
Belarus - everyone speaks Russian, but Belorussian is mandatory in schools
Ukraine - a vast number of people (maybe not majority but too many to be called a minority) speaks Russian as their first language but Ukrainian is mandatory in schools and all attempts to give Russian some sort of official status were meet with fierce opposition for no other reason than to preserve national identity
Tatarstan (not so sure about this one, also not a country) - Tatar is mandatory in schools for all the same reasons
Yes, all of these majority languages where once forced on the peoples of colonies by the empires. But all the people who were forced to learn them are now dead. So the current generations are forced to learn those original languages in the name of historical justice and other bullshit.
And what studies do you need for negative effects? The time learning those languages involuntarily is obviously not spent doing anything else. Is that not negative enough for you?
No, it is not enough for me. The same could be said of any other school subject you don't have an interest in, a sort of grown up version of "When am I ever going to use trigonometry?" complaint you hear out of school kids. But since I'm a firm believer in "historical justice and other bullshit," I think we're at an impasse here.
Well, in all seriousness, "saving a language" can mean many things, beyond "using humans as storage devices". On the one end of the scale, it can simply mean "not trying to eradicate a language". There are countless cases throughout history where speakers of central/majority languages have tried eradicating other cultures or languages, see e.g. "The termination phase" in http://galdu.org/govat/doc/mindeengelsk.pdf#19 about Saami.
Or, getting slightly more actively involved, it could mean trying to be supportive of the people who actually want to use their language – like creating software/web site localisations, book translations, spell checkers / other language tech. It doesn't have to mean forcing people to learn a language they don't want to learn, just so they can be studied by linguists :-)
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I was a bit disappointed by the "need to save cultures" paragraph as well; tighter-knit isn't necessarily better, especially not if it means active antagonism against other groups. But you'd think there would be less antagonism between groups if speakers of a non-central language have the feeling that the language they grew up learning, the language their parents spoke to them, the language that's nearest to their self-identity, is considered by the majority/central group to be somehow "worthy" (and not just something that should go away because it's an annoyance).
That is clearly not only not correct but is the opposite of the presentation in Genesis 11:4–9. This will be very clear if you could take just a few moments to go and read the story of Babel, which is a mythological account of the origin and benefits of language diversification. It is a very short story, only six verses long, that will take at most one minute to read.
The Babel story is getting misrepresented here from its clear Biblical representation. Some here are spinning as a triumph of progress and advancement through efficient communication.
In Genesis, it is given as a situation where common language allows people to display hubris while wasting effort on a completely useless project of attempting to build a tower to reach the sky. This project and its attitude is presented as clearly evil, and diversification of language, babelification, is given as a divine solution to the problem, which is presented as originating from cultural unity, common language, and concentration in a single area.
I don't see that at all. He has two arguments. The first is that a common, and distinct, language helps a culture maintain its cohesion and continuity. It's worth noting that many writers from colonized areas have commented on the irony of writing about their experience using the colonizer's language. It's also worth noting the efforts in many areas to distinguish a group's own language from other nearby languages, even mutually intelligible ones. Why would these issues come up if language didn't matter on a cultural level? To many people, loss of language and loss of culture are related. Obviously this doesn't go for everyone, and some people willingly give up their native or cultural language, but no one should ever be forced to, no more than anyone should be forced to give up their religion, way of thinking, or way of life.
The second argument is basically that languages are data points. Studying languages, especially more isolated languages that tend to be in more danger of extinction, helps us better understand linguistics and human communication. If you only know one programming language, it's much harder to learn a new one than if you've already studied 50 programming languages. This increased linguistic understanding helps us study ancient cultures. It also helps us understand language acquisition, which in turn helps us encourage the language abilities of people with linguistic difficulties. It helps us build natural language processing tools. It even helps us develop patience when dealing with people who talk about things in a significantly different way. Something that may sound blunt or crude or inappropriate can be seen in a different light if you understand that different people communicate differently.
And... if you want to get a little "out there"... If humans ever encounter intelligent extraterrestrial life, we will be much more likely to be able to decipher their communication if we've studied 6000 languages already than if we've only studied 60. Even 60 is looking somewhat ambitious for the future of language. It's not hard to imagine a time when the only remaining languages are from a handful of language families: Indo-European, Afro-Asiatic, Niger-Congo, Sino-Tibetan, Japonic, Koreanic, and Turkic.
And if that does happen, the languages that remain will also likely be significantly simplified as languages tend to be when they become widespread. That may simplify communication, but it will make it harder to study communication and how it works.
The author of this piece (John McWhorter) has written a number of truly excellent books about languages. I would strongly encourage anyone with even a passing interest in linguistics to read any of his books that strike your fancy.
As for the second argument, I agree with it. I just think the burden of studying and preserving the languages should be on those who chose to dedicate their lives to studying them, i.e. scientists like the author or enthusiasts. Not some random dude who just happened to be born in the wrong place.
But I admit I might have given this a political angle it didn't originally have.
Just a note about the Austranesian language family: it contains a large number of speakers in Indonesia/Malaysia and the Phillipines, as well as lesser groups from Madagascar, Taiwan aboriginal people, NZ Maori, and Pacific Islanders as far east as Tahiti. It's likely to be in any handful of families left that people will speak.