Yes, governments should take steps to keep threatened languages alive, because languages are relevant to history. Just as society would not tolerate a biological species of animal being extinct, there is value in society in preserving language. Languages are both historical and cultural, and there is a valid government interest in making sure the language is preserved.
I think it is important to keep as many languages alive and in use as possible. Different languages play a key role in different cultures and traditions throughout the world. I think it is important to keep these languages alive so that cultures and traditions don't die along with them.