An attempt to reverse the decline of a language
The language died with the last speaker, Dolly Pentreath, but a historian tried to record as many of her words as he could in late 1700. In the 1920s, Cornish was revived by teaching it in schools and in evening courses for adults. They have had to create many new words for modern day inventions and objects and it's impossible to know the correct pronunciation for the words.
The usage of Hebrew declined around 4000 BC and then it was reserved for Jewish religious services. Once Israel was established as a country, they made Hebrew one of their official languages because of the large Jewish population. Like Cornish, many words had to be created for modern day inventions and objects.
There is little to no native speakers left of Sanskrit but the language is still taught in schools which makes it the learned method of communication amidst Hindus. There are many attempts to revive the language among the scholar community.