Japanese, Korean, and Chinese typing is in the merged installer and setup menu
Selecting Japanese, Korean, or Chinese in the installer configures that language's input engine in pull request 14433, merged into quattro. Typing starts in Latin letters. The merge is not in version 4.0.4.
A migration installs four engines and runs the default setup: Mozc for Japanese, two-set Hangul for Korean, Pinyin for simplified Chinese, and Chewing for traditional Chinese. They run under Fcitx, the program that turns those keystrokes into characters, and the pull request says that supervision stays on. All four are on the install media, so the choice works without a network. The pull request says a user's existing engines and switching keys are kept.
An existing user turns a language on under Setup, then Typing, then Keyboard Layouts and Input Methods. Super+I cycles keyboard layouts and the configured engines together, including a mix such as English and Danish plus Japanese. The bar shows a keyboard mark only when more than one layout or engine is set. A single layout stays hidden. The shortcut still works if that mark is taken off the bar.
Japanese can use a JIS keyboard or a US keyboard. Ctrl+Space stays with the terminal, and the desktop keeps its Super shortcuts. David Heinemeier Hansson wrote that a live check walked from English through Danish, Mozc, Hangul, Pinyin, and Chewing, then back to English. He opened and merged the change.