Improve the footnote wrapping when a zh/ja lang post has English too

Ref: #320 (comment)

ox-blackfriday.el

@@ -145,12 +145,14 @@ Japanese or Korean."
         ;; Support multi-line footnote definitions by folding all
         ;; footnote definition lines into a single line as Blackfriday
         ;; does not support that.
-        (setq def (replace-regexp-in-string
-                   "\n"
-                   ;; Do not insert spaces when joining newlines for
-                   ;; CJK languages.
-                   (if is-cjk "" " ")
-                   def))
+        (setq def (if is-cjk
+                      (replace-regexp-in-string
+                       ;; Do not insert spaces when joining newlines for
+                       ;; CJK languages.
+                       "\\([[:multibyte:]]\\)[[:blank:]]*\n[[:blank:]]*\\([[:multibyte:]]\\)" "\\1\\2"
+                       def)
+                    (replace-regexp-in-string "\n" " " def)))
+
         ;; Replace multiple consecutive spaces with a single space.
         (setq def (replace-regexp-in-string "[[:blank:]]+" " " def))
         (push (cons n def) fn-alist-stripped)

test/site/content-org/all-posts.org

@@ -2605,7 +2605,13 @@ This is some text[fn:3].
 :EXPORT_FILE_NAME: multi-line-footnote-japanese
 :EXPORT_HUGO_LOCALE: ja
 :END:
-This is some text[fn:6].
+Here is a footnote where it originally had Japanese text on both
+lines[fn:6].
+
+Here is a footnote where originally the first line ended in English
+but next line started with Japanese[fn:7].
+
+Here is a footnote entirely in English[fn:3].
 ** Bind footnotes to the preceding word
 :PROPERTIES:
 :EXPORT_FILE_NAME: footnotes-bind-to-preceding-word
@@ -7534,10 +7540,14 @@ Results from static site search implemented using /Fusejs/, /jquery/
 and /mark.js/. -- [[https://gist.github.com/eddiewebb/735feb48f50f0ddd65ae5606a1cb41ae][Source]]
 * Footnotes
 
+[fn:7] English on line 1
+の Japanese on line 2
+
 [fn:6] これは
 テストです.
 
 [fn:5] See [@thompson2016].
+
 [fn:4] Even if the user has set the =HUGO_CODE_FENCE= value to =t=
 (via variable, keyword or subtree property), the Hugo =highlight=
 shortcode will be used automatically instead of code fences if either

test/site/content/posts/multi-line-footnote-japanese.md

@@ -4,6 +4,14 @@ tags = ["footnote"]
 draft = false
 +++
 
-This is some text[^fn:1].
+Here is a footnote where it originally had Japanese text on both
+lines[^fn:1].
+
+Here is a footnote where originally the first line ended in English
+but next line started with Japanese[^fn:2].
+
+Here is a footnote entirely in English[^fn:3].
 
 [^fn:1]: これはテストです.
+[^fn:2]: English on line 1 の Japanese on line 2
+[^fn:3]: This is a long footnote. It is so long that it gets auto-filled over multiple lines. But even then it should be handled fine.