Noted author and anthropologist, Wade Davis once said, “Now a language is not just a body of vocabulary or a set of grammatical rules, it’s a flash of the human spirit. It’s a vehicle for which the soul of a culture comes through to the material world. Every language in some sense is an ecosystem of ideas, a watershed of thought, an old growth forest of the mind.”
You see languages are not just a list of vocabulary, grammatical concepts and so on. It is the thought process of the people who speak or use that language for communication and transaction. It is the only communicated or documented record of the entire umbrella of the soul and success of it. That includes the geography, demographic movements, cultural evolution, medicine, economy and logic. Of course, the list is bigger but I feel these are the more important ones.
If the indigenous languages are preserved then;
A lot of traditions and rituals in different communities will become more meaningful to the younger generation. The practices would be more heart felt. For example, most of the chants and hymns in Hindu culture are mostly in Sanskrit. Now modern population has got no idea of what all those chants mean and they just go with the flow during the ceremony and rituals. If the popularity of the language was not fading, the religious references would have been more cosmic and less of doctrines. The rest you know how you can make your own judgement without getting played by the power!
A lot of medicinal and ancient mystic secrets which have the solution for our overall well being can be brought back into use for modern issues. Anything that is modern it is for us to believe. During the ancient time as we say, they thought they were more advanced and modern than their ancestors. Things have been pretty much the same through time; only the needs get different faces from time to time!
This one might be harder to quantify but preservation of indigenous languages or rather encouragement to speak indigenous languages enables speakers to use their linguistic cognition better. You see what is “I love you” in English it might be “You I love” in another language. But the whole focus will always be on the fact that its you whom I love. So the organization of information in your head is strikingly similar in any language.
Of course it is comparatively cheaper, socially acceptable and more realistic to accept English for all that esoteric academic standards and purposes. However, preservation of the indigenous language would totally increase the relevance of humanistic knowledge and moderation in the use of artificial intelligence and technological control.