Uncomfortable truth: time for developing new universal languages is over. Somebody can learn Nahuatl or whatever out of interest, but if they don't speak it to their kids (and make kids speak it between themselves), it will end with this very person.
"Grand" languages like English, Spanish, Mandarin, Russian, Arabic are gravity centers that attract and absorb dust like indigenous languages or even bigger ones like Finnish.
The process is the same: less and less content and therefore reasons to use the language, then it becomes uncool "rural thing" for young people, then their kids use it just to talk to grandmas, then it may be forcibly taught at schools, then cycle repeats with positive feedback and then it's gone and exists only in youtube channels with 10k subscribers.
So unless you push people back to their villages and fragment society, this trend won't reverse.
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