Japan Writers’ Association 日本文芸家協会 is listed on several of the publisher home pages as handling rights for many of their authors.
On their page for Copyright Clearance there is a great deal of important information for you. To the right there is a list (choice of excel or html) of the authors they represent. When you open the list you will see if they have full or partial representation for each author. Below that are excel spreadsheet files for newly added authors, authors who have canceled their contracts, and authors they used to represent who are out of copyright from 2010 on. A careful look at these pages will save you a lot of time.
Once you have determined that the author you are interested in is represented by the JWACC, you need to check and see which request form 申請フォーム (shinsei fōm) you should fill out. Most of the forms about about broadcasting, putting images or excerpts on the web, using paragraphs in exams, requests for reprints, games, etc. But no.17 is the one that you need. 許諾申請についての相談用フォーム (kyodaku shinsei ni tsuite no sōdan fōm). On this form, you designate whether you are checking about an author that they have partial representation for or something else. This is the form that I think should be used to check and see if the rights are available to translate a particular book or story of an author they represent. If anyone knows for sure, I would be very grateful for confirmation.
Just a reminder that Japanese copyright rules are 70 years after the death of the author (and not 70s after publication of the work) so any of the stories by someone like Yoshiya Nobuko who published stories in the 1920s but lived until 1973 are protected by copyright. And, yes, 吉屋信子 is represented by JWACC.
The JWACC has a pdf dated 2016 著作権Q&A 翻訳権 is covered under article 27 of the copyright law.
A translation is considered a derivative work (in Japanese 二次的使用) along with adaptation (like creating a manga based on a novel). 二次使用 and 二次的使用 are different. Niji shiyo is a reuse (publishing it in an anthology for example) but without any changes. Nijiteki shiyo is an adaptation. Good and easy explanation <a href="http://jibunkyo.main.jp/index.php/guide3" here="" at the Nihon Jido bungakusha kyokai copyright guide.