As self-translation has become a more and more common practice in our globalized world, more and more research is be done in this area. Jan Walsh Hokenson and Marcella Munson have given an excellent overview of the history and long tradition of self-translation, explaining the historical and political circumstances in the different centuries which led authors to self-translation.
If you don't have the time to read a whole book or just want to get an impression of how widespread self-translation has always been, you can also start with an article by Julio César Santoyo (written in Spanish). Santoyo aims to refute that only few authors translated their own works by listing numerous self-translators since the 14th century and claims that more research has to be done on this subject. His short overview gives you several starting points for your own research as sometimes you don't really get more information as just the fact that the author translated his own work. No languages are mentioned, neither how often the author used self-translation or if he did translate his work on his own or with the aid of a professional translator.
For further reading:
Jan Walsh Hokenson and Marcella Munson (2007): The Bilingual Text. History and Theory of Literary Self-translation. St. Jerome Publishing. 246 pages.
Julio César Santoyo (2005): Autotraducciones. In: META v50 , n3, p. 858-867.