Vim keybindings don't work with Japanese keyboard #153

Hello,

I've been investigating an issue related to the use of Japanese input sources with the Codemirror Vim extension in different browsers and environments.

I tried reproducing it on mac, using these as input sources:

• Japanese - Kana: This input source doesn't work in any browser and is even broken in the vim editor itself when used in terminal (even though there are workarounds to make it work).
• Japanese - Romaji: This behaves differently in Chrome and Safari. In Safari, it's mostly non-functional. In Chrome, pressing 'j' moves the cursor two lines down instead of one, and entering insert mode not only activates it but also adds an extra character to the text.

I tried to find out what is the cause for this, but couldn't figure it out.
Opening an issue here to track and in case you have some ideas. Thanks!