In Wales the Welsh language has had a massive revival. It's taught in schools, and a basic understanding is very common amongst younger generations.
I used Welsh, Irish, Catalan and French-in-Quebec as examples because they're all languages that declined (to varying degrees) over several centuries under (varying degrees of) government suppression, experienced a partial rebound in interest and popularity in the 20th century after government policy was changed to encourage their use, but ultimately returned to the same trend of declining usage, something like
100|
N
|\_
| \_
| \_ ____
| \_ _/ \_
| \____/ \
N_______________________
0|suppressed encouraged