Thanks! I knew this would be a problem at some point, and having introduced three new characters, you've actually contributed to the problem. :-P
You can make a quick fix yourself: just localize name + description of all your characters! Not only does that look better than the "Unknown key" message, it will also reduce the space required by the character previews, so more characters will fit into the visible space.
In the long run, I probably should make some changes to the GUI code: Adding a scrollbar to the previews, putting buttons next to the editor-mode for scrolling the previews left/right, wrapping the line after five or six previews, so there are multiple rows of character previews followed by one row with the buttons for god/editor mode …
Another idea: Remove the preview of the currently selected character (so the characters at the top will be just the available characters) and add a preview of the current character (or the one last used before the player entered god/editor mode) below, next to the god/editor mode buttons.
I'm not sure yet what's the best way. The number of alternative characters has grown over the past two years. It's still relatively small (<10), but why shouldn't there be 20 or more in the future? That's obviously something I'd have to prepare for.
If you or somebody else has ideas, I'm open to suggestions! :-)