If Google shows Japanese titles and thousands of Japanese pages under your domain, your site has been hit by the Japanese keyword hack, not a translation glitch. A hidden script is generating those pages for search engines only, and they will keep coming back until you remove the code and the backdoor behind it.
The short answer
- Japanese pages in Google under your domain almost always mean the Japanese keyword hack: a server-side script generating cloaked spam for crawlers.
- Deleting the visible pages does nothing. Remove the generator, the backdoor and the stolen credentials first, or the spam returns within hours.
- Don't block spam URLs in robots.txt. Let Googlebot see 404 or 410 Gone, then use Search Console Removals as a temporary stopgap.
- File a reconsideration request only if Search Console shows a manual action, and only after the site is verifiably clean.