Japanese characters?

[User Ribbon]

On Thu, Jan 21, 2021 at 10:11:27PM +0100, meine wrote:
> 
> by accident I discovered that I can compose Japanese kana (hiragana,
> katakana) in mutt. I wonder if this is a feature, or somewhere lurking
> in my mutt and FreeBSD setup (although I only use default software and
> settings). I have NL language settings for UTF-8 on a user level in my
> system, and use Vim as the editor for my emails. BTW, this described
> here doesn't work in Vim, but only in mutt.

I'm using mutt and compose Japanese text with emacs.
but mutt is not original, Japanese patch applied.
(https://ja.osdn.net/projects/mutt-j/)

> 
> It works like this:
> 
> typing a letter, then backspace and then another letter -- just making a
> typo and correcting it.
> 
> m <backspace> e --> め (hiragana `me`)
> 
> M <backspace> e -- メ (katakana `me`)
> 
> it just works with all characters, only the plain `a` in both writings I
> cannot find.

Does this behavior occur in mutt's builtin editor, or does it occur in vim?