I recently revisted two places and I had contrasting impressions of the ways that minority languages were/were not being maintained.
The first place was Guangzhou, which I had first visited in 1987. At that time, it seemed very much dominated by Guangzhou dialect rather than Putonghua. Now, it seems that the Guangzhou dialect is heard less although it is common in some contexts like restaurants.
The second place was Toulouse where I was struck by the use of dual dialect road signs and underground announcements althhough I did not hear much dialect use in the streets. Perhaps my experience was too limited as I doubt there would be such a promotion if there was not much use of or interest in the language.