In Danbooru, where the tags are mostly copied over from, including deprecations, Japanese text is also deprecated. This is due to vast majority of posts and their commentaries being written in Japanese in Danbooru.
This shouldn't carry over to AIBooru however. English commentary might be as popular if not more popular than what Japanese commentary would be. Same for translated & translation request having only 41 posts in total compared English text which is just under 200 posts.
So in short, Japanese text is in the same importance level as other languages so there's no reason to "default" it to that, and these tags should be kept undeprecated and populated.