“The number of speakers of the vast majority, or maybe even all, languages of Russia’s minorities is declining rapidly and that’s no secret,” linguist and co-founder of the Country of Languages, a digital platform for language activists, Vasiliy Kharitonov said.
“But I’m not sure we can assess these dynamics through censuses.”
While official statistics might help to identify trends, they fail to capture the real number of active language users, according to Kharitonov. 
For example, the 2021 census suggested the number of speakers of Nanai, once common in Siberia and northeast China, includes about 1,000 speakers under the age of 19. 
“I haven’t yet met a single person of that age [under 19] who could be definitively labeled as a proficient speaker,” said Kharitonov, who previously worked on a program promoting the Nanai language among children. 
Instead, the census data reflects a growing interest in Nanai rather than any real knowledge or day-to-day use, according to Kharitonov.  

https://www.themoscowtimes.com/2023/03/13/languages-in-russia-disappearing-faster-than-data-suggests-activists-warn-a80432