@hongminhee (4) seems good. It'll be no different than having mixed-language content. E.g. the ruby tags can be extended as such:

```
<ruby lang="ja">日本語<rp>(</rp><rt lang="ko">일본어</rt><rp>)</rp></ruby>
```

But, I think some folks might want to separate them with (1), so that people can subscribe to one account but filter by language ("Change subscribed language" in individual profile pages on Mastodon).