I would be interested to find a plain text editor that provides a mode for vertical text.
Chinese and Japanese can both be written either left-to-right in rows going from top to bottom, or top-to-bottom in columns going from right to left. There are editors for formatted documents which support these, such as Microsoft Word.
But from time to time I have a need to type plain old unformatted text vertically in Chinese and Japanese.
Whereas a formatted document editor would allow both horizontal and vertical within a document using its layout and markup systems, a plain text editor would just have it as a viewing mode.
(much like being able to select a font or turning word-wrap on and off.)
It doesn't matter how inline English or other languages are rendered
(letters rotated 90° or not), though more options are better than fewer.
It should work with the standard IMEs that ship with the OS.
Unicode should be supported, including supplementary plane support.
(UTF-8 or UTF-16 but must not mangle surrogate pairs or save as ASCII silently converting everything to
Really should have installer and user interface in English.
Even though I know how to type several languages, I can't actually speak or read them so menus, preferences, installer, etc should be available also in English.
I have also wanted to type vertical Mongolian script recently and it is a bit different: top-to-bottom in columns going from left to right. An editor which supported this mode would be best of all, but editors without it are also acceptable.
I'm using Windows 7 but I have a preference for open source, cross platform software.