CJK characters render with the wrong regional glyph on Linux

That should work. Where are you adding it? The conventional way to do this is with inline CSS for a specific field replacement –

<div lang="ja">
   {{JapaneseText}}
</div>

You don’t say what version of Anki you’re using, but for other suggestions, see – Font differences between 25.09 and 25.09.2 .