True Left

A historic example, rather than an example of ongoing activism:

In Paraguay the Guarani language is one of the official languages and spoken by over half the population.
https://en.wikipedia.org/wiki/Guarani_language

Southern Brazil was on the same course, but was thwarted:

The Língua Geral Paulista (Paulista General language), or Tupi Austral (Southern Tupi), was a Tupi-based trade language of São Vicente and the upper Tietê River, in the Brazilian state of São Paulo. In the 17th century, it was widely spoken in the municipality São Paulo and spread to neighboring regions. Starting in 1750, orders from Marquis of Pombal forced Portuguese to be taught to Paulista children in schools. Língua Geral Paulista subsequently lost ground to Portuguese and eventually became extinct.

https://en.wikipedia.org/wiki/L%C3%ADngua_Geral_of_S%C3%A3o_Paulo