By some miraculous coincidence I managed to find a partial Japanese translation of NSMBe b376 on ancolog's dead site. b376 is old but I updated the file to work in the newest version of NSMBe5.3.
Original site: https://web.archive.org/web/20160525032253/http://kinokosouko.blog.fc2.com/
Original download link: http://ux.getuploader.com/kinoko_sky/download/15/nsmb-editor-376.rar
Updated download link: https://nsmbhd.net/file/eAK2DA3HTnzQZh1i/Japanese.ini (updated with parasol'n's translations)
I take no credit for the translation (I can't even read Japanese).
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Nothing to say, so jadnjkfmnjamnfjkldnajfnjkanfjdksan jsdnvj m.

 Keeper helped me get my hands on another Japanese translation of NSMBe by a user known as parasol'n. It's a more complete translation than the one by ancolog, however it was made in mid 2011 for a version of NSMBe that is now wildly outdated. Thankfully, I was able to port a good part of it to modern NSMBe and combine it with the other translation. I could probably port more of it with a bit of effort but there's only so much I can do for a language that I don't even speak. This one also came with a fully translated sprite database, but the sprite database changed so much since 2011 that I didn't even want to try to update it for new NSMBe, so I'll just leave it here and let you pray that it works/isn't too incomplete.
Original site: http://paramario.blog41.fc2.com/blog-entry-29.html
Original download link: http://www.axfc.net/uploader/Sc/so/256484.rar
Updated download link (combined with ancolog's translation): https://nsmbhd.net/file/eAK2DA3HTnzQZh1i/Japanese.ini
Sprite Database: https://nsmbhd.net/file/csqZfrSHpTB0mJf0/spritedata.txt
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Nothing to say, so jadnjkfmnjamnfjkldnajfnjkanfjdksan jsdnvj m.