Is there any Anime/Manga adaptation with source material from outside of Japan? Were there ever any instances of something taken from outside of Japan (book, comic, literature) that was turned into anime or manga?
Of course there are.  I would give you some examples


Les Miserables



  Les Misérables (French pronunciation: ​[le mizeʁabl(ə)]) is a French
  historical novel by Victor Hugo, first published in 1862, that is
  considered one of the greatest novels of the 19th century. In the
  English-speaking world, the novel is usually referred to by its
  original French title. However, several alternatives have been used,
  including The Miserables, The Wretched, The Miserable Ones, The Poor
  Ones, The Wretched Poor, The Victims and The Dispossessed.1
  Beginning in 1815 and culminating in the 1832 June Rebellion in Paris,
  the novel follows the lives and interactions of several characters,
  particularly the struggles of ex-convict Jean Valjean and his
  experience of redemption.2
  
  Examining the nature of law and grace, the novel elaborates upon the
  history of France, the architecture and urban design of Paris,
  politics, moral philosophy, antimonarchism, justice, religion, and the
  types and nature of romantic and familial love. Les Misérables has
  been popularized through numerous adaptations for the stage,
  television, and film, including a musical and a film adaptation of
  that musical.




It has a manga and anime adaptation


Les Miserables Anime (aired in 2007)

Les Miserables Manga (was published from 2013 to 2016 )



And many more ( this one that cross my mind, so i couldn't give more )

Update answer based your request


Deltora Quest(based wikipedia, it was published around 2000 to 2005 )



  The Deltora Quest series is the collective title for three series of
  children's literature fantasy books, written by Australian author
  Emily Rodda. It follows the adventures of three companions as they
  journey across the fictitious land of Deltora, endeavoring to recover
  the seven gems stolen from the magical Belt of Deltora and defeat
  allies of the evil Shadow Lord. The series was first published in
  Australia in 2000, and has since been published in more than 30
  countries. As of February 2010, the series has sold over 15 million
  copies worldwide, including 2 million in Australia. It is published
  by Scholastic in Australia and the United States. In most countries,
  the series is illustrated by Marc McBride.
  
  The series consists of fifteen books: the first eight comprise the
  Deltora Quest series, the next three comprise the Deltora Shadowlands
  series (also known as Deltora Quest 2, Deltora II or Deltora 2) and
  the final four comprise the Dragons of Deltora series (also known as
  Deltora Quest 3, Deltora III or Deltora 3). There are also six other
  official bonus books to the series: The Deltora Book of Monsters,
  Tales of Deltora, The Authorised Ultimate Deltora Quiz Book, How to
  Draw Deltora Monsters, How to Draw Deltora Dragons and Other Creatures
  and Secrets of Deltora. An anime adaptation of the series aired on
  Japanese television from 6 January 2007 to 29 March 2008. An anime
  adaptation also aired in Australia for a short time. A Nintendo DS
  game for Deltora Quest has also been made in Japan. In 2011 Emily
  Rodda announced in an interview as part of the Australian Council of
  the Arts Get Reading! Program that she had sold the movie rights of
  the Deltora Quest series to a "prominent Hollywood production
  company."



Picture taken from pinterest

It has a manga and anime adaptation


Deltora Quest manga


Deltora Quest Anime




If you want to see more about this kind of topic, you could find it on MAL Discussion