There is a difference between a text viewer and an ebook/text file viewer. A text viewer is more to just glance at a settings file.
Also, by using the Search tool, I found this:
https://gbatemp.net/threads/release-3ds-ebook-reader.399257 . Unfortunately the thread is locked due to the fact that OP was trying to take credit for someone else's release (Bad OP!) but the thing itself looks interesting. It was made by
@AlbertoSONIC according to last page, so I'm paging him on whether he ever actually released it (as I can't find a release thread).
EDIT: So after doing a bit of research (AKA type his name in GitHub search for the code) I found the repository. Although he seems to have abandoned it (last notice in Dec2015) someone called @reworks has continued the project:
https://github.com/reworks/3DS_eBook_Reader