Nǁng or Nǁŋǃke, which is also known as Nǀu, is the only surviving member of the !Ui branch of the Tuu or Khoisan language family. It was declared extinct in 1973, but in the 1990s the South African San Institute managed to find 25 people who could speak or understand the language. Today there are fewer than 10 speakers left in South Africa and Botswana, but they use Afrikaans or Tswana as their every day languages rather than Nǁng.
Under apartheid people who spoke Nǁng had to hide their language and identity from others, including their children. They adopted other languages, such as Afrikaans, and their children did not acquire even a passive knowledge of Nǁng.
Source: http://www.kalaharipeoples.org/academic/nuu/Segments.html (includes recordings)
Information about the Nǁng language