Twenty-five languages a year are expected to die every year for the next hundred years, about a quarter of all languages in existence today. Some money is being spent to, at least, develop some record that they ever existed -- a record of their vocabularies, grammars and sounds, but they will die never the less.
There are only about 231 languages spoken by 2 million people or more in the world. Moreover, even many of these languages are mere secondary languages even in the countries where they are spoken. To take European examples, because they are familiar: Germany is home to Upper Saxon (2 million), as well as German (95 million). Italy is home to Emiliano-Romagnolo (2 million), Venetian (2 million), Piemontese (3 million), Sicilian (4 million), Napoletano (7 million), and Lombard (9 million), as well as Italian (61 million). Spain is home to Galician (3 million), and Catalan (6 million), as well as Spanish (322 million) (the figures are all worldwide numbers).
I doubt that there are many Upper Saxon speakers who don't also speak German, and I doubt that there are many Venetian speakers who don't also speak Italian. In the same way, almost all speakers of Welsh and Gaelic can also speak English.
When almost all speakers of a language are also fluent in another common language, its raison d'etre fades. It becomes an elaborate hobby and tradition. When your language has only five fluent speakers, how different is what you are doing in passing it on to your children from raising your children to speak Klingon? In the most prominent example in the United States, it may be a noble and culturally meaningful thing to learn to speak Navajo. It may even have niche applications -- as the Code Talkers proved. But, there are virtually no Navajo speakers who do not also speak English or Spanish, and those very few who speak only Navajo, if there are any, live a very restricted existence.
It is remarkable that the other 9,750 languages out there have survived as long as they have managed to survive. Modern society can't handle the situation that Papua New Guinea has where there are 820 languages among fewer than 5.5 million people, an average of fewer than 7,000 people each. Imagine what Colorado would be like if every neighborhood and county had its own language.
Vital languages, languages that thrive rather than merely exist, need authors and poets and newscasters and political speeches and schools and so much more. They need compact regions where they are the dominant language, the language in which people think and communicate with each other and do business and learn new things. It takes hundreds of thousands of listeners to make a viable television station. It takes tens of thousands of listeners to make a viable radio station or newspaper. It takes several thousand book purchases a year to support a single author, and many authors to create a real literary climate. A language has to be the dominant one in a state or province or area of comparable political authority, for legislators to carry on business in a particular language. The number of languages that can meet these thresholds are in the hundreds and not the thousands.
Languages which are not vital languages are really all endangered, although some may be dying more quickly than others. Numbers don't tell the entire story. Lombard is spoken by many more people than Hebrew, but Hebrew, because it is the primary language of a nation state, has brighter prospects than Lombard.
It is sad to see the richest part of so many cultures vanish from the Earth, but I see no way to prevent it from happening.