Dead Languages:
As time passes, things change. Some of them lose their value while others become more important. History is filled with examples of things that were very popular once but then faded into nothingness. It gets to the point where no one knows those things existed except historians. But there are a few things that we manage to preserve by documenting them. They went extinct in the past couple of centuries, which is why recording them was easier. Take Latin, for instance, which is a dead language, but we have enough material on it that people can still learn it. Maybe some of our Latin dictionaries are not complete, but that doesn’t mean that the language is gone completely. However, there is one dead language that has been revived successfully, and that is Hebrew.