I download these packages:

    $ doas pkg_add ubuntu-fonts uim uim-chewing uim-gtk \
     uim-gtk3 zh-fonts-arphicttf zh-fonts-kc zh-libchewing \
     zh-libpinyin zh-wqy-bitmapfont zh-wqy-zenhei-ttf


This includes the font packs and UIM input engine for zhuyin (chewing) and pinyin.

Inside ~/.profile, I put this line:

    export LC_CTYPE=en_US.UTF-8


You will also want to run that command in your current terminal.

When you need to type Chinese in firefox, I run:

    $ uim-toolbar-gtk3


When I need to type Chinese in Xterm, I type:

    $ uim-fep -u chewing


To toggle between Chinese and English, type ctrl+space.

For xterm, I add the following lines:

    XTerm*forcePackedFont: true
    XTerm*cjkWidth: false
    XTerm*mkWidth: true
    xterm*faceName: DejaVu Sans Mono
    xterm*faceSize: 25


Change xterm*faceSize: 25 to match your desired font size. Open a new xterm window to see the new settings.