bug#25685: fill-paragraph vs. \n vs. Chinese / English boundaries

[Katsumi Yamaoka <yamaoka@jpl.org>]

On Mon, 13 Feb 2017 09:22:46 +0900, Katsumi Yamaoka wrote:
> I first tried:

> * lisp/textmodes/fill.el (fill-delete-newlines):
> Don't delete leading and trailing space from CJK word.

In Japan some people write an English word in Japanese text with
spaces, and others do it with no space:

日本語と English の混在
日本語とEnglishの混在

For the later case, some word processor separates them with thin
spaces automatically, but Emacs doesn't (I'm not wrong, am I?).
So, I am the former.  Anyway, if the patch is applied, it would
embarrass the later people, i.e.:

寿限無寿限無五劫の擦り切れ海砂利水魚の水行末雲来末風来末
eating寝るplaceに住む処やぶら小路の藪柑子パイポパイポ...
↓
寿限無寿限無五劫の擦り切れ海砂利水魚の水行末雲来末風来末 eating寝る
placeに住む処やぶら小路の藪柑子パイポパイポ...

So, there may want to be a user option, of which the default value
doesn't change the present behavior.  Is there a good name for it?

fill-multilinguala-words-with-spaces
                  text?
fill-separate-words-with-spaces-in-multilingual-text
fill-words-with-spaces-in-multilingual-text

↓describe its meaning in doc string
fill-words-with-spaces
fill-paragraph-with-spaces ← not necessarily used for paragraph?