Improve the optional translation of quotes

Fix several problems with the recently-added custom variable
help-quote-translation where the code would quote inconsistently
in help buffers.  Add support for quoting 'like this', which
is common in other GNU programs in ASCII environments.  Change
help-quote-translation to use more mnemonic values: values are now the
initial quoting char, e.g., (setq help-quote-translation ?`) gets the
traditional Emacs help-buffer quoting style `like this'.  Change the
default behavior of substitute-command-keys to match what's done in
set-locale-environment, i.e., quote ‘like this’ if displayable,
'like this' otherwise.
* doc/lispref/help.texi (Keys in Documentation): Document
new behavior of substitute-command-keys, and document
help-quote-translation.
* doc/lispref/tips.texi (Documentation Tips):
Mention the effect of help-quote-translation.
* etc/NEWS: Mention new behavior of substitute-command-keys,
and merge help-quote-translation news into it.
When talking about doc strings, mention new ways to type quotes.
* lisp/cedet/mode-local.el (overload-docstring-extension):
Revert my recent change to this function, which shouldn't be
needed as the result is a doc string.
* lisp/cedet/mode-local.el (mode-local-print-binding)
(mode-local-describe-bindings-2):
* lisp/cedet/srecode/srt-mode.el (srecode-macro-help):
* lisp/cus-theme.el (describe-theme-1):
* lisp/descr-text.el (describe-text-properties-1, describe-char):
* lisp/emacs-lisp/cl-generic.el (cl--generic-describe):
* lisp/emacs-lisp/eieio-opt.el (eieio-help-class)
(eieio-help-constructor):
* lisp/emacs-lisp/package.el (describe-package-1):
* lisp/faces.el (describe-face):
* lisp/help-fns.el (help-fns--key-bindings)
(help-fns--compiler-macro, help-fns--parent-mode)
(help-fns--obsolete, help-fns--interactive-only)
(describe-function-1, describe-variable):
* lisp/help.el (describe-mode):
Use substitute-command-keys to ensure a more-consistent quoting
style in help buffers.
* lisp/cus-start.el (standard):
Document new help-quote-translation behavior.
* lisp/emacs-lisp/lisp-mode.el (lisp-fdefs):
* lisp/help-mode.el (help-xref-symbol-regexp, help-xref-info-regexp)
(help-xref-url-regexp):
* lisp/international/mule-cmds.el (help-xref-mule-regexp-template):
* lisp/wid-edit.el (widget-documentation-link-regexp):
Also match 'foo', in case we're in a help buffer generated when
help-quote-translation is ?'.
* src/doc.c: Include disptab.h, for DISP_CHAR_VECTOR.
(LEFT_SINGLE_QUOTATION_MARK, uLSQM0, uLSQM1, uLSQM2, uRSQM0)
(uRSQM1, uRSQM2, LSQM, RSQM): New constants.
(Fsubstitute_command_keys): Document and implement new behavior.
(Vhelp_quote_translation): Document new behavior.

19 files changed, 213 insertions, 122 deletions

diff --git a/doc/lispref/help.texi b/doc/lispref/help.texi
index ce29f3f5bc3..44a680c4a22 100644
--- a/doc/lispref/help.texi
+++ b/doc/lispref/help.texi
@@ -319,10 +319,22 @@ specifies @var{mapvar}'s value as the keymap for any following
 @samp{\[@var{command}]} sequences in this documentation string.
 
 @item `
-(grave accent) stands for a left single quotation mark (@samp{‘}).
+(grave accent) stands for a left quote, and alters the interpretation
+of the next unmatched apostrophe.
 
 @item '
-(apostrophe) stands for a right single quotation mark (@samp{’}) if
+(apostrophe) stands for a right quote if preceded by grave accent and
+there are no intervening apostrophes.  Otherwise, apostrophe stands
+for itself.
+
+@item ‘
+(left single quotation mark) stands for a left quote.
+
+@item ’
+(right single quotation mark) stands for a right quote.
+
+@item '
+(apostrophe) stands for a right quote if
 preceded by grave accent and there are no intervening apostrophes.
 Otherwise, apostrophe stands for itself.
 
@@ -335,6 +347,19 @@ and @samp{\=\=} puts @samp{\=} into the output.
 @strong{Please note:} Each @samp{\} must be doubled when written in a
 string in Emacs Lisp.
 
+@defvar help-quote-translation
+@cindex curved quotes
+The value of this variable specifies the style
+@code{substitute-command-keys} uses when generating left and right
+quotes.  If the variable's value is @code{?‘} (U+2018 LEFT SINGLE
+QUOTATION MARK), the style is @t{‘like this’} with curved single
+quotes.  If the value is @code{?'} (apostrophe), the style is @t{'like
+this'} with apostrophes.  If the value is @code{?`} (grave accent),
+the style is @t{`like this'} with grave accent and apostrophe.  The
+default value @code{nil} means to use curved single quotes if
+displayable and apostrophes otherwise.
+@end defvar
+
 @defun substitute-command-keys string
 This function scans @var{string} for the above special sequences and
 replaces them by what they stand for, returning the result as a string.
diff --git a/doc/lispref/tips.texi b/doc/lispref/tips.texi
index 9144497d5f1..7107bb45872 100644
--- a/doc/lispref/tips.texi
+++ b/doc/lispref/tips.texi
@@ -671,9 +671,11 @@ Documentation strings can also use an older single-quoting convention,
 which quotes symbols with grave accent @t{`} and apostrophe
 @t{'}: @t{`like-this'} rather than @t{‘like-this’}.  This
 older convention was designed for now-obsolete displays in which grave
-accent and apostrophe were mirror images.  Documentation in this older
-convention is converted to the standard convention when it is copied
-into a help buffer.  @xref{Keys in Documentation}.
+accent and apostrophe were mirror images.
+
+Documentation using either convention is converted to the user's
+preferred format when it is copied into a help buffer.  @xref{Keys in
+Documentation}.
 
 @cindex hyperlinks in documentation strings
 Help mode automatically creates a hyperlink when a documentation string
diff --git a/etc/NEWS b/etc/NEWS
index 1611c7a7926..bab1b41e759 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -845,11 +845,16 @@ when signaling a file error.  For example, it now reports "Permission
 denied" instead of "permission denied".  The old behavior was problematic
 in languages like German where downcasing rules depend on grammar.
 
-** (substitute-command-keys "`foo'") now returns "‘foo’".
-That is, it replaces grave accents by left single quotation marks, and
-apostrophes that match grave accents by right single quotation marks.
-As before, isolated apostrophes and characters preceded by \= are
-output as-is.
+** substitute-command-keys now replaces quotes.
+That is, it replaces left single quotation marks (‘) by left quotes
+and right single quotation marks (’) by right quotes.  It also
+replaces grave accents by left quotes, and apostrophes that match
+grave accents by right quotes.  As before, isolated apostrophes and
+characters preceded by \= are output as-is.  Left and right quotes are
+determined by new custom variable ‘help-quote-translation’.  ?‘ means
+quote ‘like this’, ?' means quote 'like this', ?` means quote `like
+this', and nil (default) means quote ‘like this’ if displayable and
+'like this' otherwise.
 
 +++
 ** The character classes [:alpha:] and [:alnum:] in regular expressions
@@ -956,10 +961,10 @@ directory at point.
 ** Documentation strings now support quoting with curved single quotes
 ‘like-this’ in addition to the old style with grave accent and
 apostrophe `like-this'.  The new style looks better on today's displays.
-When an old-style string is copied to a help buffer it is converted to
-the new style.
-
-** New option `help-quote-translation'.
+In the new Electric Quote mode, you can enter curved single quotes
+into documentation by typing ` and '.  Outside Electric Quote mode,
+you can enter them by typing ‘C-x 8 [’ and ‘C-x 8 ]’, or (if your Alt
+key works) by typing ‘A-[’ and ‘A-]’.
 
 +++
 ** Time-related changes:
diff --git a/lisp/cedet/mode-local.el b/lisp/cedet/mode-local.el
index 35363337aee..3bdc3ea6155 100644
--- a/lisp/cedet/mode-local.el
+++ b/lisp/cedet/mode-local.el
@@ -598,16 +598,15 @@ PROMPT, INITIAL, HIST, and DEFAULT are the same as for `completing-read'."
 (defun overload-docstring-extension (overload)
   "Return the doc string that augments the description of OVERLOAD."
   (let ((doc "\n\This function can be overloaded\
- with ‘define-mode-local-override’.")
+ with `define-mode-local-override'.")
         (sym (overload-obsoleted-by overload)))
     (when sym
-      (setq doc (format "%s\nIt has made the overload ‘%s’ obsolete since %s."
+      (setq doc (format "%s\nIt has made the overload `%s' obsolete since %s."
                         doc sym (get sym 'overload-obsoleted-since))))
     (setq sym (overload-that-obsolete overload))
     (when sym
-      (setq doc (format
-                 "%s\nThis overload is obsolete since %s;\nuse ‘%s’ instead."
-                 doc (get overload 'overload-obsoleted-since) sym)))
+      (setq doc (format "%s\nThis overload is obsolete since %s;\nUse `%s' instead."
+                        doc (get overload 'overload-obsoleted-since) sym)))
     doc))
 
 (defun mode-local-augment-function-help (symbol)
@@ -630,9 +629,10 @@ SYMBOL is a function that can be overridden."
 (defun mode-local-print-binding (symbol)
   "Print the SYMBOL binding."
   (let ((value (symbol-value symbol)))
-    (princ (format "\n     ‘%s’ value is\n       " symbol))
+    (princ (format (substitute-command-keys "\n     ‘%s’ value is\n       ")
+                   symbol))
     (if (and value (symbolp value))
-        (princ (format "‘%s’" value))
+        (princ (format (substitute-command-keys "‘%s’") value))
       (let ((pt (point)))
         (pp value)
         (save-excursion
@@ -690,7 +690,7 @@ SYMBOL is a function that can be overridden."
       )
      ((symbolp buffer-or-mode)
       (setq mode buffer-or-mode)
-      (princ (format "‘%s’\n" buffer-or-mode))
+      (princ (format (substitute-command-keys "‘%s’\n") buffer-or-mode))
       )
      ((signal 'wrong-type-argument
               (list 'buffer-or-mode buffer-or-mode))))
@@ -700,7 +700,7 @@ SYMBOL is a function that can be overridden."
     (while mode
       (setq table (get mode 'mode-local-symbol-table))
       (when table
-        (princ (format "\n- From ‘%s’\n" mode))
+        (princ (format (substitute-command-keys "\n- From ‘%s’\n") mode))
         (mode-local-print-bindings table))
       (setq mode (get-mode-local-parent mode)))))
 
diff --git a/lisp/cedet/srecode/srt-mode.el b/lisp/cedet/srecode/srt-mode.el
index fbc56357b1c..48f055561ea 100644
--- a/lisp/cedet/srecode/srt-mode.el
+++ b/lisp/cedet/srecode/srt-mode.el
@@ -258,9 +258,9 @@ we can tell font lock about them.")
             (when (class-abstract-p C)
               (throw 'skip nil))
 
-            (princ "‘")
+            (princ (substitute-command-keys "‘"))
             (princ name)
-            (princ "’")
+            (princ (substitute-command-keys "’"))
             (when (slot-exists-p C 'key)
               (when key
                 (princ " - Character Key: ")
diff --git a/lisp/cus-start.el b/lisp/cus-start.el
index 12def4c4148..7cf5ce736bd 100644
--- a/lisp/cus-start.el
+++ b/lisp/cus-start.el
@@ -223,9 +223,10 @@ Leaving \"Default\" unchecked is equivalent with specifying a default of
              ;; doc.c
              (help-quote-translation help
                                      (choice
-                                      (const :tag "No translation" nil)
-                                      (const :tag "Translate curly single quotes to ASCII" traditional)
-                                      (const :tag "Translate ASCII single quotes to curly" prefer-unicode))
+                                      (character :tag "Quote ‘like this’" :value ?‘)
+                                      (character :tag "Quote 'like this'" :value ?\')
+                                      (character :tag "Quote `like this'" :value ?\`)
+                                      (const :tag "Quote ‘like this’ if displyable, 'like this' otherwise" nil))
                                      "25.1")
              ;; dosfns.c
              (dos-display-scancodes display boolean)
diff --git a/lisp/cus-theme.el b/lisp/cus-theme.el
index 1321fbc4b7e..bc221e17c4b 100644
--- a/lisp/cus-theme.el
+++ b/lisp/cus-theme.el
@@ -492,10 +492,10 @@ It includes all faces in list FACES."
                          '("" "c")))
         doc)
     (when fn
-      (princ " in ‘")
+      (princ (substitute-command-keys " in ‘"))
       (help-insert-xref-button (file-name-nondirectory fn)
                                'help-theme-def fn)
-      (princ "’"))
+      (princ (substitute-command-keys "’")))
     (princ ".\n")
     (if (custom-theme-p theme)
         (progn
diff --git a/lisp/descr-text.el b/lisp/descr-text.el
index c8641aed8bb..a0b9ddfe2c9 100644
--- a/lisp/descr-text.el
+++ b/lisp/descr-text.el
@@ -161,8 +161,11 @@ otherwise."
       ;; Buttons
       (when (and button (not (widgetp wid-button)))
         (newline)
-        (insert "Here is a ‘" (format "%S" button-type)
-                "’ button labeled ‘" button-label "’.\n\n"))
+        (insert (substitute-command-keys "Here is a ‘")
+                (format "%S" button-type)
+                (substitute-command-keys "’ button labeled ‘")
+                button-label
+                (substitute-command-keys "’.\n\n")))
       ;; Overlays
       (when overlays
         (newline)
@@ -738,8 +741,9 @@ relevant to POS."
                       (when face
                         (insert (propertize " " 'display '(space :align-to 5))
                                 "face: ")
-                        (insert (concat "‘" (symbol-name face) "’"))
-                        (insert "\n")))))
+                        (insert (substitute-command-keys "‘")
+                                (symbol-name face)
+                                (substitute-command-keys "’\n"))))))
               (insert "these terminal codes:\n")
               (dotimes (i (length disp-vector))
                 (insert (car (aref disp-vector i))
diff --git a/lisp/emacs-lisp/cl-generic.el b/lisp/emacs-lisp/cl-generic.el
index 96b86aa21cc..5923e4db996 100644
--- a/lisp/emacs-lisp/cl-generic.el
+++ b/lisp/emacs-lisp/cl-generic.el
@@ -876,11 +876,11 @@ Can only be used from within the lexical body of a primary or around method."
                                    (cl--generic-method-specializers method)))
                    (file (find-lisp-object-file-name met-name 'cl-defmethod)))
               (when file
-                (insert " in ‘")
+                (insert (substitute-command-keys " in ‘"))
                 (help-insert-xref-button (help-fns-short-filename file)
                                          'help-function-def met-name file
                                          'cl-defmethod)
-                (insert "’.\n")))
+                (insert (substitute-command-keys "’.\n"))))
             (insert "\n" (or (nth 2 info) "Undocumented") "\n\n")))))))
 
 ;;; Support for (head <val>) specializers.
diff --git a/lisp/emacs-lisp/eieio-opt.el b/lisp/emacs-lisp/eieio-opt.el
index 11d99849a97..6cd6813956a 100644
--- a/lisp/emacs-lisp/eieio-opt.el
+++ b/lisp/emacs-lisp/eieio-opt.el
@@ -90,11 +90,11 @@ If CLASS is actually an object, then also display current values of that object.
           " class")
   (let ((location (find-lisp-object-file-name class 'eieio-defclass)))
     (when location
-      (insert " in ‘")
+      (insert (substitute-command-keys " in ‘"))
       (help-insert-xref-button
        (help-fns-short-filename location)
        'eieio-class-def class location 'eieio-defclass)
-      (insert "’")))
+      (insert (substitute-command-keys "’"))))
   (insert ".\n")
   ;; Parents
   (let ((pl (eieio-class-parents class))
@@ -103,10 +103,10 @@ If CLASS is actually an object, then also display current values of that object.
       (insert " Inherits from ")
       (while (setq cur (pop pl))
         (setq cur (eieio--class-name cur))
-        (insert "‘")
+        (insert (substitute-command-keys "‘"))
         (help-insert-xref-button (symbol-name cur)
                                  'help-function cur)
-        (insert (if pl "’, " "’")))
+        (insert (substitute-command-keys (if pl "’, " "’"))))
       (insert ".\n")))
   ;; Children
   (let ((ch (eieio-class-children class))
@@ -114,10 +114,10 @@ If CLASS is actually an object, then also display current values of that object.
     (when ch
       (insert " Children ")
       (while (setq cur (pop ch))
-        (insert "‘")
+        (insert (substitute-command-keys "‘"))
         (help-insert-xref-button (symbol-name cur)
                                  'help-function cur)
-        (insert (if ch "’, " "’")))
+        (insert (substitute-command-keys (if ch "’, " "’"))))
       (insert ".\n")))
   ;; System documentation
   (let ((doc (documentation-property class 'variable-documentation)))
@@ -130,9 +130,9 @@ If CLASS is actually an object, then also display current values of that object.
     (when generics
       (insert (propertize "Specialized Methods:\n\n" 'face 'bold))
       (dolist (generic generics)
-        (insert "‘")
+        (insert (substitute-command-keys "‘"))
         (help-insert-xref-button (symbol-name generic) 'help-function generic)
-        (insert "’")
+        (insert (substitute-command-keys "’"))
         (pcase-dolist (`(,qualifiers ,args ,doc)
                        (eieio-method-documentation generic class))
           (insert (format " %s%S\n" qualifiers args)
@@ -245,11 +245,11 @@ are not abstract."
         (setq location
               (find-lisp-object-file-name ctr def)))
       (when location
-        (insert " in ‘")
+        (insert (substitute-command-keys " in ‘"))
         (help-insert-xref-button
          (help-fns-short-filename location)
          'eieio-class-def ctr location 'eieio-defclass)
-        (insert "’"))
+        (insert (substitute-command-keys "’")))
       (insert ".\nCreates an object of class " (symbol-name ctr) ".")
       (goto-char (point-max))
       (if (autoloadp def)
diff --git a/lisp/emacs-lisp/lisp-mode.el b/lisp/emacs-lisp/lisp-mode.el
index ab01a109b7a..72a23cfdfc6 100644
--- a/lisp/emacs-lisp/lisp-mode.el
+++ b/lisp/emacs-lisp/lisp-mode.el
@@ -403,8 +403,8 @@
          ;; Words inside \\[] tend to be for `substitute-command-keys'.
          ("\\\\\\\\\\[\\(\\(?:\\sw\\|\\s_\\)+\\)\\]"
           (1 font-lock-constant-face prepend))
-         ;; Words inside ‘’ and `' tend to be symbol names.
-         ("[`‘]\\(\\(?:\\sw\\|\\s_\\)\\(?:\\sw\\|\\s_\\)+\\)['’]"
+         ;; Words inside ‘’ and '' and `' tend to be symbol names.
+         ("['`‘]\\(\\(?:\\sw\\|\\s_\\)\\(?:\\sw\\|\\s_\\)+\\)['’]"
           (1 font-lock-constant-face prepend))
          ;; Constant values.
          ("\\_<:\\(?:\\sw\\|\\s_\\)+\\_>" 0 font-lock-builtin-face)
@@ -452,8 +452,8 @@
          ;; Erroneous structures.
          (,(concat "(" cl-errs-re "\\_>")
            (1 font-lock-warning-face))
-         ;; Words inside ‘’ and `' tend to be symbol names.
-         ("[`‘]\\(\\(?:\\sw\\|\\s_\\)\\(?:\\sw\\|\\s_\\)+\\)['’]"
+         ;; Words inside ‘’ and '' and `' tend to be symbol names.
+         ("['`‘]\\(\\(?:\\sw\\|\\s_\\)\\(?:\\sw\\|\\s_\\)+\\)['’]"
           (1 font-lock-constant-face prepend))
          ;; Constant values.
          ("\\_<:\\(?:\\sw\\|\\s_\\)+\\_>" 0 font-lock-builtin-face)
diff --git a/lisp/emacs-lisp/package.el b/lisp/emacs-lisp/package.el
index 074d3e8dda3..62900e08360 100644
--- a/lisp/emacs-lisp/package.el
+++ b/lisp/emacs-lisp/package.el
@@ -2173,17 +2173,18 @@ will be deleted."
                                    "Installed"
                                  (capitalize status)) ;FIXME: Why comment-face?
                                'font-lock-face 'font-lock-comment-face))
-           (insert " in ‘")
+           (insert (substitute-command-keys " in ‘"))
            ;; Todo: Add button for uninstalling.
            (help-insert-xref-button (abbreviate-file-name
                                      (file-name-as-directory pkg-dir))
                                     'help-package-def pkg-dir)
            (if (and (package-built-in-p name)
                     (not (package-built-in-p name version)))
-               (insert "’,\n             shadowing a "
+               (insert (substitute-command-keys
+                        "’,\n             shadowing a ")
                        (propertize "built-in package"
                                    'font-lock-face 'font-lock-builtin-face))
-             (insert "’"))
+             (insert (substitute-command-keys "’")))
            (if signed
                (insert ".")
              (insert " (unsigned)."))
diff --git a/lisp/faces.el b/lisp/faces.el
index 4366c0b9f23..ac6486ee46c 100644
--- a/lisp/faces.el
+++ b/lisp/faces.el
@@ -1428,10 +1428,12 @@ If FRAME is omitted or nil, use the selected frame."
                   (when alias
                     (setq face alias)
                     (insert
-                     (format "\n  %s is an alias for the face ‘%s’.\n%s"
+                     (format (substitute-command-keys
+                              "\n  %s is an alias for the face ‘%s’.\n%s")
                              f alias
                              (if (setq obsolete (get f 'obsolete-face))
-                                 (format "  This face is obsolete%s; use ‘%s’ instead.\n"
+                                 (format (substitute-command-keys
+                                          "  This face is obsolete%s; use ‘%s’ instead.\n")
                                          (if (stringp obsolete)
                                              (format " since %s" obsolete)
                                            "")
@@ -1449,12 +1451,13 @@ If FRAME is omitted or nil, use the selected frame."
                     (help-xref-button 1 'help-customize-face f)))
                 (setq file-name (find-lisp-object-file-name f 'defface))
                 (when file-name
-                  (princ "Defined in ‘")
+                  (princ (substitute-command-keys "Defined in ‘"))
                   (princ (file-name-nondirectory file-name))
-                  (princ "’")
+                  (princ (substitute-command-keys "’"))
                   ;; Make a hyperlink to the library.
                   (save-excursion
-                    (re-search-backward "‘\\([^‘’]+\\)’" nil t)
+                    (re-search-backward
+                     (substitute-command-keys "‘\\([^‘’]+\\)’") nil t)
                     (help-xref-button 1 'help-face-def f file-name))
                   (princ ".")
                   (terpri)
diff --git a/lisp/help-fns.el b/lisp/help-fns.el
index 80f30e88fa4..9541d4797b4 100644
--- a/lisp/help-fns.el
+++ b/lisp/help-fns.el
@@ -306,7 +306,9 @@ suitable file is found, return nil."
             (when remapped
               (princ "Its keys are remapped to ")
               (princ (if (symbolp remapped)
-                         (concat "‘" (symbol-name remapped) "’")
+                         (concat (substitute-command-keys "‘")
+                                 (symbol-name remapped)
+                                 (substitute-command-keys "’"))
                        "an anonymous command"))
               (princ ".\n"))
 
@@ -340,16 +342,18 @@ suitable file is found, return nil."
       (insert "\nThis function has a compiler macro")
       (if (symbolp handler)
           (progn
-            (insert (format " ‘%s’" handler))
+            (insert (format (substitute-command-keys " ‘%s’") handler))
             (save-excursion
-              (re-search-backward "‘\\([^‘’]+\\)’" nil t)
+              (re-search-backward (substitute-command-keys "‘\\([^‘’]+\\)’")
+                                  nil t)
               (help-xref-button 1 'help-function handler)))
         ;; FIXME: Obsolete since 24.4.
         (let ((lib (get function 'compiler-macro-file)))
           (when (stringp lib)
-            (insert (format " in ‘%s’" lib))
+            (insert (format (substitute-command-keys " in ‘%s’") lib))
             (save-excursion
-              (re-search-backward "‘\\([^‘’]+\\)’" nil t)
+              (re-search-backward (substitute-command-keys "‘\\([^‘’]+\\)’")
+                                  nil t)
               (help-xref-button 1 'help-function-cmacro function lib)))))
       (insert ".\n"))))
 
@@ -404,13 +408,13 @@ suitable file is found, return nil."
                           (get function
                                'derived-mode-parent))))
     (when parent-mode
-      (insert "\nParent mode: ‘")
+      (insert (substitute-command-keys "\nParent mode: ‘"))
       (let ((beg (point)))
         (insert (format "%s" parent-mode))
         (make-text-button beg (point)
                           'type 'help-function
                           'help-args (list parent-mode)))
-      (insert "’.\n"))))
+      (insert (substitute-command-keys "’.\n")))))
 
 (defun help-fns--obsolete (function)
   ;; Ignore lambda constructs, keyboard macros, etc.
@@ -426,7 +430,9 @@ suitable file is found, return nil."
       (when (nth 2 obsolete)
         (insert (format " since %s" (nth 2 obsolete))))
       (insert (cond ((stringp use) (concat ";\n" use))
-                    (use (format ";\nuse ‘%s’ instead." use))
+                    (use (format (substitute-command-keys
+                                  ";\nuse ‘%s’ instead.")
+                                 use))
                     (t "."))
               "\n"))))
 
@@ -462,7 +468,8 @@ FILE is the file where FUNCTION was probably defined."
                           (format ";\nin Lisp code %s" interactive-only))
                          ((and (symbolp 'interactive-only)
                                (not (eq interactive-only t)))
-                          (format ";\nin Lisp code use ‘%s’ instead."
+                          (format (substitute-command-keys
+                                   ";\nin Lisp code use ‘%s’ instead.")
                                   interactive-only))
                          (t "."))
                    "\n")))))
@@ -531,7 +538,8 @@ FILE is the file where FUNCTION was probably defined."
                  ;; Aliases are Lisp functions, so we need to check
                  ;; aliases before functions.
                  (aliased
-                  (format "an alias for ‘%s’" real-def))
+                  (format (substitute-command-keys "an alias for ‘%s’")
+                          real-def))
                  ((autoloadp def)
                   (format "%s autoloaded %s"
                           (if (commandp def) "an interactive" "an")
@@ -565,21 +573,24 @@ FILE is the file where FUNCTION was probably defined."
       (with-current-buffer standard-output
         (save-excursion
           (save-match-data
-            (when (re-search-backward "alias for ‘\\([^‘’]+\\)’" nil t)
+            (when (re-search-backward (substitute-command-keys
+                                       "alias for ‘\\([^‘’]+\\)’")
+                                      nil t)
               (help-xref-button 1 'help-function real-def)))))
 
       (when file-name
-        (princ " in ‘")
+        (princ (substitute-command-keys " in ‘"))
         ;; We used to add .el to the file name,
         ;; but that's completely wrong when the user used load-file.
         (princ (if (eq file-name 'C-source)
                    "C source code"
                  (help-fns-short-filename file-name)))
-        (princ "’")
+        (princ (substitute-command-keys "’"))
         ;; Make a hyperlink to the library.
         (with-current-buffer standard-output
           (save-excursion
-            (re-search-backward "‘\\([^‘’]+\\)’" nil t)
+            (re-search-backward (substitute-command-keys "‘\\([^‘’]+\\)’")
+                                nil t)
             (help-xref-button 1 'help-function-def function file-name))))
       (princ ".")
       (with-current-buffer (help-buffer)
@@ -712,14 +723,17 @@ it is displayed along with the global value."
 
               (if file-name
                   (progn
-                    (princ " is a variable defined in ‘")
+                    (princ (substitute-command-keys
+                            " is a variable defined in ‘"))
                     (princ (if (eq file-name 'C-source)
                                "C source code"
                              (file-name-nondirectory file-name)))
-                    (princ "’.\n")
+                    (princ (substitute-command-keys "’.\n"))
                     (with-current-buffer standard-output
                       (save-excursion
-                        (re-search-backward "‘\\([^‘’]+\\)’" nil t)
+                        (re-search-backward (substitute-command-keys
+                                             "‘\\([^‘’]+\\)’")
+                                            nil t)
                         (help-xref-button 1 'help-variable-def
                                           variable file-name)))
                     (if valvoid
@@ -849,7 +863,8 @@ if it is given a local binding.\n")))
               ;; Mention if it's an alias.
               (unless (eq alias variable)
                 (setq extra-line t)
-                (princ (format "  This variable is an alias for ‘%s’.\n"
+                (princ (format (substitute-command-keys
+                                "  This variable is an alias for ‘%s’.\n")
                                alias)))
 
               (when obsolete
@@ -858,7 +873,8 @@ if it is given a local binding.\n")))
                 (if (nth 2 obsolete)
                     (princ (format " since %s" (nth 2 obsolete))))
                 (princ (cond ((stringp use) (concat ";\n  " use))
-                             (use (format ";\n  use ‘%s’ instead."
+                             (use (format (substitute-command-keys
+                                           ";\n  use ‘%s’ instead.")
                                           (car obsolete)))
                              (t ".")))
                 (terpri))
@@ -889,14 +905,15 @@ if it is given a local binding.\n")))
                               ;; Otherwise, assume it was set directly.
                               (setq file (car file)
                                     dir-file nil)))
-                        (princ (if dir-file
-                                   "by the file\n  ‘"
-                                 "for the directory\n  ‘"))
+                        (princ (substitute-command-keys
+                                (if dir-file
+                                    "by the file\n  ‘"
+                                  "for the directory\n  ‘")))
                         (with-current-buffer standard-output
                           (insert-text-button
                            file 'type 'help-dir-local-var-def
                            'help-args (list variable file)))
-                        (princ "’.\n")))
+                        (princ (substitute-command-keys "’.\n"))))
                   (princ "  This variable's value is file-local.\n")))
 
               (when (memq variable ignored-local-variables)
@@ -910,8 +927,9 @@ variable.\n"))
                 (princ "  This variable may be risky if used as a \
 file-local variable.\n")
                 (when (assq variable safe-local-variable-values)
-                  (princ "  However, you have added it to \
-‘safe-local-variable-values’.\n")))
+                  (princ (substitute-command-keys
+                          "  However, you have added it to \
+‘safe-local-variable-values’.\n"))))
 
               (when safe-var
                 (setq extra-line t)
@@ -919,7 +937,8 @@ file-local variable.\n")
                 (princ "if its value\n  satisfies the predicate ")
                 (princ (if (byte-code-function-p safe-var)
                            "which is a byte-compiled expression.\n"
-                         (format "‘%s’.\n" safe-var))))
+                         (format (substitute-command-keys "‘%s’.\n")
+                                 safe-var))))
 
               (if extra-line (terpri))
               (princ "Documentation:\n")
diff --git a/lisp/help-mode.el b/lisp/help-mode.el
index 3fc0ad2b403..6454eed27bd 100644
--- a/lisp/help-mode.el
+++ b/lisp/help-mode.el
@@ -322,7 +322,7 @@ Commands:
                     "\\(source \\(?:code \\)?\\(?:of\\|for\\)\\)\\)"
                     "[ \t\n]+\\)?"
                     ;; Note starting with word-syntax character:
-                    "[`‘]\\(\\sw\\(\\sw\\|\\s_\\)+\\)['’]"))
+                    "['`‘]\\(\\sw\\(\\sw\\|\\s_\\)+\\)['’]"))
   "Regexp matching doc string references to symbols.
 
 The words preceding the quoted symbol can be used in doc strings to
@@ -338,11 +338,11 @@ when help commands related to multilingual environment (e.g.,
 
 (defconst help-xref-info-regexp
   (purecopy
-   "\\<[Ii]nfo[ \t\n]+\\(node\\|anchor\\)[ \t\n]+[`‘]\\([^'’]+\\)['’]")
+   "\\<[Ii]nfo[ \t\n]+\\(node\\|anchor\\)[ \t\n]+['`‘]\\([^'’]+\\)['’]")
   "Regexp matching doc string references to an Info node.")
 
 (defconst help-xref-url-regexp
-  (purecopy "\\<[Uu][Rr][Ll][ \t\n]+[`‘]\\([^'’]+\\)['’]")
+  (purecopy "\\<[Uu][Rr][Ll][ \t\n]+['`‘]\\([^'’]+\\)['’]")
   "Regexp matching doc string references to a URL.")
 
 ;;;###autoload
diff --git a/lisp/help.el b/lisp/help.el
index 2bf53c09b05..7a3460c1b3d 100644
--- a/lisp/help.el
+++ b/lisp/help.el
@@ -964,12 +964,14 @@ documentation for the major and minor modes of that buffer."
         (let* ((mode major-mode)
                (file-name (find-lisp-object-file-name mode nil)))
           (when file-name
-            (princ (concat " defined in ‘" (file-name-nondirectory file-name)
-                           "’"))
+            (princ (concat (substitute-command-keys " defined in ‘")
+                           (file-name-nondirectory file-name)
+                           (substitute-command-keys "’")))
             ;; Make a hyperlink to the library.
             (with-current-buffer standard-output
               (save-excursion
-                (re-search-backward "‘\\([^‘’]+\\)’" nil t)
+                (re-search-backward (substitute-command-keys "‘\\([^‘’]+\\)’")
+                                    nil t)
                 (help-xref-button 1 'help-function-def mode file-name)))))
         (princ ":\n")
         (princ (documentation major-mode)))))
diff --git a/lisp/international/mule-cmds.el b/lisp/international/mule-cmds.el
index e56fcebfc26..16c1003960a 100644
--- a/lisp/international/mule-cmds.el
+++ b/lisp/international/mule-cmds.el
@@ -177,7 +177,7 @@
                     "\\(charset\\)"
                     "\\)\\s-+\\)?"
                     ;; Note starting with word-syntax character:
-                    "[`‘]\\(\\sw\\(\\sw\\|\\s_\\)+\\)['’]")))
+                    "['`‘]\\(\\sw\\(\\sw\\|\\s_\\)+\\)['’]")))
 
 (defun coding-system-change-eol-conversion (coding-system eol-type)
   "Return a coding system which differs from CODING-SYSTEM in EOL conversion.
diff --git a/lisp/wid-edit.el b/lisp/wid-edit.el
index 295e2aada2a..f7d8964c9fc 100644
--- a/lisp/wid-edit.el
+++ b/lisp/wid-edit.el
@@ -2863,7 +2863,7 @@ The following properties have special meanings for this widget:
   :type 'boolean
   :group 'widget-documentation)
 
-(defcustom widget-documentation-link-regexp "[`‘]\\([^\n `'‘’]+\\)['’]"
+(defcustom widget-documentation-link-regexp "['`‘]\\([^\n `'‘’]+\\)['’]"
   "Regexp for matching potential links in documentation strings.
 The first group should be the link itself."
   :type 'regexp
diff --git a/src/doc.c b/src/doc.c
index 81b1354668f..2ea416f3a2b 100644
--- a/src/doc.c
+++ b/src/doc.c
@@ -32,6 +32,7 @@ along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
 #include "lisp.h"
 #include "character.h"
 #include "buffer.h"
+#include "disptab.h"
 #include "keyboard.h"
 #include "keymap.h"
 
@@ -683,6 +684,18 @@ the same file name is found in the `doc-directory'.  */)
   return unbind_to (count, Qnil);
 }
 
+/* Declare named constants for U+2018 LEFT SINGLE QUOTATION MARK and
+   U+2019 RIGHT SINGLE QUOTATION MARK, which have UTF-8 encodings
+   "\xE2\x80\x98" and "\xE2\x80\x99", respectively.  */
+enum
+  {
+    LEFT_SINGLE_QUOTATION_MARK = 0x2018,
+    uLSQM0 = 0xE2, uLSQM1 = 0x80, uLSQM2 = 0x98,
+    uRSQM0 = 0xE2, uRSQM1 = 0x80, uRSQM2 = 0x99,
+  };
+static unsigned char const LSQM[] = { uLSQM0, uLSQM1, uLSQM2 };
+static unsigned char const RSQM[] = { uRSQM0, uRSQM1, uRSQM2 };
+
 DEFUN ("substitute-command-keys", Fsubstitute_command_keys,
        Ssubstitute_command_keys, 1, 1, 0,
        doc: /* Substitute key descriptions for command names in STRING.
@@ -699,8 +712,10 @@ summary).
 Each substring of the form \\=\\<MAPVAR> specifies the use of MAPVAR
 as the keymap for future \\=\\[COMMAND] substrings.
 
-Each \\=` is replaced by ‘.  Each ' preceded by \\=` and without
-intervening ' is replaced by ’.
+Each \\=‘ and \\=’ are replaced by left and right quote.  Each \\=` is
+replaced by left quote, and each ' preceded by \\=` and without
+intervening ' is replaced by right quote.  Left and right quote
+characters are specified by ‘help-quote-translation’.
 
 \\=\\= quotes the following character and is discarded; thus,
 \\=\\=\\=\\= puts \\=\\= into the output, \\=\\=\\=\\[ puts \\=\\[ into the output, and
@@ -719,7 +734,7 @@ Otherwise, return a new string.  */)
   ptrdiff_t bsize;
   Lisp_Object tem;
   Lisp_Object keymap;
-  unsigned char *start;
+  unsigned char const *start;
   ptrdiff_t length, length_byte;
   Lisp_Object name;
   struct gcpro gcpro1, gcpro2, gcpro3, gcpro4;
@@ -735,6 +750,21 @@ Otherwise, return a new string.  */)
   name = Qnil;
   GCPRO4 (string, tem, keymap, name);
 
+  enum { unicode, grave_accent, apostrophe } quote_translation = unicode;
+  if (EQ (Vhelp_quote_translation, make_number ('`')))
+    quote_translation = grave_accent;
+  else if (EQ (Vhelp_quote_translation, make_number ('\'')))
+    quote_translation = apostrophe;
+  else if (NILP (Vhelp_quote_translation)
+           && DISP_TABLE_P (Vstandard_display_table))
+    {
+      Lisp_Object dv = DISP_CHAR_VECTOR (XCHAR_TABLE (Vstandard_display_table),
+                                         LEFT_SINGLE_QUOTATION_MARK);
+      if (VECTORP (dv) && ASIZE (dv) == 1
+          && EQ (AREF (dv, 0), make_number ('\'')))
+        quote_translation = apostrophe;
+    }
+
   multibyte = STRING_MULTIBYTE (string);
   nchars = 0;
 
@@ -932,38 +962,39 @@ Otherwise, return a new string.  */)
             strp = SDATA (string) + idx;
           }
         }
-      else if (EQ (Vhelp_quote_translation, Qprefer_unicode)
-               && (strp[0] == '`'))
+      else if (strp[0] == '`' && quote_translation == unicode)
         {
           in_quote = true;
-          start = (unsigned char *) "\xE2\x80\x98"; /* ‘ */
+          start = LSQM;
         subst_quote:
           length = 1;
           length_byte = 3;
           idx = strp - SDATA (string) + 1;
           goto subst;
         }
-      else if (EQ (Vhelp_quote_translation, Qprefer_unicode)
-               && (strp[0] == '\'' && in_quote))
+      else if (strp[0] == '`' && quote_translation == apostrophe)
+        {
+          *bufp++ = '\'';
+          strp++;
+          nchars++;
+          changed = true;
+        }
+      else if (strp[0] == '\'' && in_quote)
         {
           in_quote = false;
-          start = (unsigned char *) "\xE2\x80\x99"; /* ’ */
+          start = RSQM;
           goto subst_quote;
         }
-
-      else if (EQ (Vhelp_quote_translation, Qtraditional)
-               && (strp[0] == 0xE2)
-               && (strp[1] == 0x80)
-               && ((strp[2] == 0x98)      /* curly opening quote */
-                   || (strp[2] == 0x99))) /* curly closing quote */
+      else if (strp[0] == uLSQM0 && strp[1] == uLSQM1
+               && (strp[2] == uLSQM2 || strp[2] == uRSQM2)
+               && quote_translation != unicode)
         {
-          start = (strp[2] == 0x98) ? "`" : "'";
-          length = 1;
-          length_byte = 1;
-          idx = strp - SDATA (string) + 3;
-          goto subst;
+          *bufp++ = (strp[2] == uLSQM2 && quote_translation == grave_accent
+                     ? '`' : '\'');
+          strp += 3;
+          nchars++;
+          changed = true;
         }
-
       else if (! multibyte)             /* just copy other chars */
         *bufp++ = *strp++, nchars++;
       else
@@ -1005,15 +1036,13 @@ syms_of_doc (void)
   Vbuild_files = Qnil;
 
   DEFVAR_LISP ("help-quote-translation", Vhelp_quote_translation,
-               doc: /* How to translate quotes for display in *Help*.
-If the value is nil (default), no translation is done.
-If it's the symbol `traditional', any occurrences of the curly quotes
-are translated to their ASCII "equivalents", GRAVE and APOSTROPHE.
-If it's the symbol `prefer-unicode', any matched pairs of GRAVE and
-APOSTROPHE will get translated into the "equivalent" curly quotes.
-
-Note that any translation done is done in a fresh copy of the doc
-string, and doesn't overwrite the original characters. */);
+               doc: /* Style to use for single quotes in help.
+The value is a left single quote character of some style.
+Quote \\=‘like this\\=’ if the value is ?\\=‘ (left single quotation mark).
+Quote 'like this' if the value is ?' (apostrophe).
+Quote \\=`like this' if the value is ?\\=` (grave accent).
+The default value is nil, which means quote with left single quotation mark
+if displayable, and with apostrophe otherwise.  */);
   Vhelp_quote_translation = Qnil;
 
   defsubr (&Sdocumentation);