Endangered languages

An endangered language is a language whose number of native speakers decreases, and at this age of globalisation, neocolonialism and linguicide, that is happening at an accelerated rate. The language shift often occurs when the new generations do not learn their heritage language, but opt for languages that are rather associated with social and economic power, or are simply more widely spoken. There are precise levels of a language being considered endangered until it is extinct. The first one is when a language is considered vulnerable, i.e. most children speak the language, but it is forbidden in certain domains. This is an estimation from year 2018 on what are the most endangered languages today:

https://www.independent.co.uk/news/science/endangered-languages-dead-listen-speakers-audio-belarusian-wiradjuri-cornish-a8268196.html 

 There many associations that work on preserving, revitalising and/or documenting them, like this one:

http://www.endangeredlanguages.com/. 

However, the total number of endangered languages today is around 3000. There are around 6000 to 7000 languages spoken in the world today, and it is considered that by 2100, 50% to 90% of those will be extinct. 

http://chartsbin.com/view/1339. 

So, what are your thoughts on this? Do you prefer global language(s), or keeping the linguistic diversity as it is? I mean as language learners, we need languages to learn, but do we need languages that are in use or would you learn or have you ever learnt one that has been or is facing extinction? 

Have you yourself ever experienced anything like this? Having your own language facing extinction? 

What do you think about this subject? 

I'm pro-language diversity. Frankly, moving towards a global language is just frightening. Whenever I think of the world moving towards a global language, I think of the dystopian novel, Brave New World, where they locked up Shakespeare, and found new ways to simplify language, and shrink vocabulary. For me, the novel really highlights how we need complex language, because complex languages, with all its difficulties and nuances, can help us describe a larger spectrum of human experience. The more we reduce it into one thing, the more we take away from the world we live in. 

I spent quite a number of years teaching US undergraduates, and one of my great frustrations with them, is their very, very limited vocabulary. Sure, they can talk, but their analysis and understanding of situations tends to be very simplistic, because they do not have the vocabulary to explain complexities.

I did not grow up speaking an endangered language (Cantonese), but Cantonese speakers in Singapore are not very common. I am actually glad my grandparents actively kept my family Cantonese (many Singaporean Chinese families opt not to do that, prioritizing English/Mandarin instead). A happy result of that is, I ended up being very rooted in the culture. By comparison, my friends' parents who opted for learning "useful" languages - they can't communicate with their grandparents, nor do they feel tied to any particular culture. 

I know some words from an extinct language, although I guess there's no real reason for anyone to learn that language, unless you study that period in Vietnamese. Nom (https://en.wikipedia.org/wiki/Ch%E1%BB%AF_N%C3%B4m) is this interesting hybrid script developed between the 15th - 19th centuries. It uses parts of the Chinese script, to basically express Vietnamese. It got phased out when Alexandre de Rhodes developed the Latin script for Vietnamese. There are less than 20 people in the world today who can still read it. 

Thank you meifeng, for your extensive and thorough reply! I appreciate it greatly, lots to learn from :)