n. The pirating of a foreign language comic book or similar graphic work by scanning the images and then translating the text.
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Since the mid-90s, when manga was just entering Westerners’ consciousness, factions of scanlators have been illicitly editing and circulating Japanese manga abroad. …

The painstaking art of scanlation rose out of the desire for American fans to read Japanese manga without waiting — possibly forever — for publishers to release official translations of their favorite comics.
—Cecilia D'Anastasio, “The Invisible Labor Economy Behind Pirated Japanese Comics,” Motherboard, April 09, 2015
Their next step: serve notice to websites that post and torrent unauthorized fan-translations (a.k.a. "scanlations") of anime and manga series that MAG Project intends to "massively delete" unauthorized copies of 580 anime/manga series owned by over 40 Japanese manga/anime companies from the Internet.
—Deb Aoki, “Japanese Manga, Anime Firms Debut Latest Antipiracy Project,” Publisher's Weekly, August 06, 2014
Kodansha has traditionally disseminated English versions of its manga series through printed comic books, but fans overseas usually have to wait “three to 12 months” to get hold of them after their Japan release, said Kodansha senior manager Tatsuya Morimoto.

This frustration has prompted impatient manga fans to chase quicker translations. The work of scanlators is distributed online “the same day as the official release, sometimes even a few days earlier than that,” Morimoto said. …The process of illegally scanning and then translating manga is known as “scanlation.”
—Tomohiro Osaki, “Kodansha manga to get same-day global release,” The Japan Times, October 29, 2013
2001 (earliest)
Well, first of all a manga scanslation is a scan of a famous manga that has the japanese text edited and changed into its english translation.
—Pointless, “manga scanslation fans,” Pinoy Exchange, October 11, 2001
A scanlation (or scanslation, a variant that is less popular, harder to say, but more comprehensible at first glance) is also called a mangascan (since the Japanese comic books, er, sorry, graphic novels, known as manga are the prime targets of scanlators), a scantrad (where "trad" comes from the French traduction, "translation"), a fansub, or a fanscan (although that term is most often used for a simple scan of a graphic work without the translation). There is a scarily comprehensive history of scanlation available at the website Inside Scanlation. Many thanks to Mark Worden for spying this term.