Náhuatl and Mayan Language Renaissance Occurring in Mexico

I always pay attention to efforts of restoration for endangered languages. Unfortunately, it seems to be an awfully difficult thing to do. In my home country, Ireland, we have been trying for around a century to restore/preserve Irish. But it has gone fairly poorly. It seems that falling below a critical mass of speakers, the language is nearly always considered 'useless'/'ancient'.

It seems to be very common across countries to have a bi-lingual population. But this is almost always the case where the native language is globally uncommon. So the population see the value of learning English/Spanish etc.

It also appears to be possible to keep languages healthy, active when there are many competing, but regional languages, not used anywhere else.

But it seems near impossible to revive a language where the majority already speak a globally useful language.

The alternative, unfortunately, seems to be to force the language through authoritarianism, like in the case of hebrew.

A counter to this that I'm aware of is Ukrainian and Polish. The soviet union tried to exterminate both during its heyday yet they've mostly completely revived despite the effort.

Hindi is probably another example of a language that the british empire tried to exterminate yet it has seen a pretty decent resurgence.

I don't think any of these languages really stayed around via force. They simply had a critical mass of speakers that never went away.

For Irish and Welsh, the British empire arguably committed a genocide to eliminate them. It similarly happened to native american tribes in the US and canada.

By my estimation, the two things that kill a language is the death of the native speakers of that language (discussed above) and the evolution of a language past what native speakers would recognize (Old/proto english and Latin for example).

USSR didn't try to "exterminate" Ukrainian, where did you get this? We spoke Ukrainian all my childhood, it was taught at school, there were TV shows, magazines and newspapers in Ukrainian. It was alive and very actively used, at least in 80's.