See :
https://www.techjockey.com/blog/top-7-best-plagiarism-checker-software-2019
It shows you top 15 best plagiarism detection and remover tools in 2021 with more details .
And it shows you list of tools with languages supported .
In that list
Turnitin plagiarism checker ( software ) allows japanese language .
or
Try -
SmallSeoTools ,
SmallSEOTools. This plagiarism checker tool allows you to check up to 1000 words per search for free. The tool is available in English, Chinese, Russian, Italian, French, Portuguese, Spanish, German, and Japanese languages.
See :
https://smallseotools.com/plagiarism-checker/#:~:text=FEATURES OF OUR PLAGIARISM CHECKER
It shows you more details about above tool with some list of features , in that list 7th is about Multiple Languages .
Hope this Helps !
