Ubuntu – Japanese IME clueless about certain words

This seems to be mostly expected behaviour. When ibus is active and one, say, moves up to the menu or exits input mode, ibus switches to input method off since it no longer sees a gui element with focus and where entering text is possible. The error message you saw ("no focused input context") is consistent with this. Ibus stays on when you go back to the text window without having performed a command because the ibus context is still alive. The bug is that the ibus context is killed when you do perform an action and follow that with a click in the text window. You're still in insert mode, but the ibus context is dead, you need to turn ibus on again. This doesn't happen in programs like LibreOffice.

I imagine the bug comes from the way vim uses a special insert mode rather than a standard gui event model. Clicking in a text window would normally set the focus on the text area, but here it doesn't. To make it work we need an add-on like ibus-el for emacs. I'm not sure where you should file a bug for this.

For a work around, I think the best thing to do is set a shortcut to enable ibus in the ibus preferences. From the ibus menu > preferences > General tab > enable box. A good one seems to be Ctrl-p since that is right next to the i for enabling input mode and the [ you may be using to exit input mode. I keeps you fingers in the same area. When you're back in the text area, a quick flick with you fingers is much easier than moving the mouse up and clicking twice.

In short, you don't want to use the im-config utility to change input methods.

Set the default input method from System Settings >> Language Support >> Default input method

After that, both input method setup and keyboard layout setup are now in System Settings >> Text Entry.

These changes seem to have caused some problems for Ibus. Assuming you have ibus-anthy installed, if you don't see Anthy in the list of input methods in Text Entry, go ahead and reinstall Ibus with sudo apt-get install --reinstall ibus and reboot.

I had similar problems but Anthy is now working fine after reinstalling Ibus.

Anthy has it's own setting for the keyboard layout that it uses.

1) In Text Entry, make sure your German keyboard is at the top of the list of input methods. This will make it the system default keyboard.

2) Highlight Anthy and click the the toolbox/configuration button that appears down by the keyboard button. This opens the Anthy settings.

3) Go to the tab called Typing Method. Change the keyboard layout to Default (which will now be German).

4) Be sure to hit the Apply button, before hitting OK.