A settlement on a remote island off of Australia's Northern Coast called the Warruwi Community consists of 500 people who speak 9 different languages. Although there are 9 languages that coexist with each other, all 500 people are able to understand each other, even with the language barrier. This is what linguists call "receptive multilingualism." People speak only the language they're allowed to speak, but can understand all the 8 different languages when they are spoken to them.
An academic at Cambridge taught himself to speak ancient Babylonian and has started a campaign to revive the language 2,000 years after it died out. Dr. Worthington has been teaching himself the language since 2000 and although he can speak, he is nowhere near being fluent in the language.
As of lately in New Zealand, the Maori language is making a comeback. It wasn't spoken for a long time because as it started to die out, many people didn't understand it so they just stopped speaking it. Recently however, the people of Maori ancestry have started to embrace their roots and have started to revive the language.
This article discusses the often assumed theory that children who learn a foreign language before they are 10 are more likely to master it than those who learn the new language as adults. MIT scientists have found through a study that although it is indeed beneficial to start learning a foreign language earlier, there is a large number of adults who outperformed native speakers. When given the same amount of time, the top 25% of people who learned the language when they were over 20 do just as well as the average person who started before they were 10.