I suppose that you just installed kubuntu 11.10 in your box, and english is your default system language.

1. Install the following packages: ibus, ibus-anthy, ibus-gtk, ibus-m17n
2. Go to the “K” menu -> applications -> system -> input setting framework
3. A box will show up with the ibus configuration options (and maybe asking you if it should start ibus, say yes)
4. configure your desired shortcuts in the “general” tab. Make sure to configure keys for “enable-disable” and “next input method”. In the “input methods” tab, add “Japanese->anthy” and “other->latin pre”
5. Close the configuration screen. Right-click on the ibus icon in your tray bar (a little keyboard with a ball) and select “restart” — you are good to go!

I always had difficulty getting both japanese and portuguese to work in my systems, it has become so easy now! How far have we come :-)