Drop duplicate vietnamese-tcvn coding system

* lisp/language/vietnamese.el (vietnamese-vscii): Update docstring.
(vietnamese-tcvn, tcvn, tcvn-5712): Make them aliases of
vietnamese-vscii.
("Vietnamese"): Drop vietnamese-tcvn from coding-system values.
Update docstring.

* etc/NEWS: Announce this change.

2 files changed, 22 insertions, 19 deletions

diff --git a/etc/NEWS b/etc/NEWS
index 39b4a35930a..7b521f3e6fe 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -665,6 +665,15 @@ previous behavior of showing 'U' in the mode line for 'koi8-u':
 
     (coding-system-put 'koi8-u :mnemonic ?U)
 
+---
+** 'vietnamese-tcvn' is now a coding system alias for 'vietnamese-vscii'.
+VSCII-1 and TCVN-5712 are different names for the same character
+encoding.  Therefore, the duplicate coding system definition has been
+dropped in favor of an alias.
+
+The mode-line mnemonic for 'vietnamese-vscii' and its aliases is the
+lowercase letter 'v'.
+
 +++
 ** Infinities and NaNs no longer act as symbols on non-IEEE platforms.
 On old platforms like the VAX that do not support IEEE floating-point,
diff --git a/lisp/language/vietnamese.el b/lisp/language/vietnamese.el
index bd0b3c5ae3e..e439a2c3851 100644
--- a/lisp/language/vietnamese.el
+++ b/lisp/language/vietnamese.el
@@ -28,8 +28,8 @@
 
 ;;; Commentary:
 
-;; For Vietnamese, the character sets VISCII, VSCII and TCVN-5712 are
-;; supported.
+;; For Vietnamese, the coding systems VISCII, VSCII-1 (TCVN-5712),
+;; VIQR and windows-1258 are supported.
 
 ;;; Code:
 
@@ -44,13 +44,16 @@
 (define-coding-system-alias 'viscii 'vietnamese-viscii)
 
 (define-coding-system 'vietnamese-vscii
-  "8-bit encoding for Vietnamese VSCII-1."
+  "8-bit encoding for Vietnamese VSCII-1 (TCVN-5712)."
   :coding-type 'charset
   :mnemonic ?v
   :charset-list '(vscii)
   :suitable-for-file-name t)
 
 (define-coding-system-alias 'vscii 'vietnamese-vscii)
+(define-coding-system-alias 'vietnamese-tcvn 'vietnamese-vscii)
+(define-coding-system-alias 'tcvn 'vietnamese-vscii)
+(define-coding-system-alias 'tcvn-5712 'vietnamese-vscii)
 
 ;; (make-coding-system
 ;;  'vietnamese-vps 4 ?p
@@ -74,7 +77,7 @@
 (set-language-info-alist
  "Vietnamese" '((charset viscii)
                 (coding-system vietnamese-viscii vietnamese-vscii
-                               vietnamese-tcvn vietnamese-viqr windows-1258)
+                               vietnamese-viqr windows-1258)
                 (nonascii-translation . viscii)
                 (coding-priority vietnamese-viscii)
                 (input-method . "vietnamese-viqr")
@@ -83,12 +86,12 @@
                 (sample-text . "Vietnamese (Tiếng Việt)     Chào bạn")
                 (documentation . "\
 For Vietnamese, Emacs uses special charsets internally.
-They can be decoded from and encoded to VISCII, VSCII, TCVN-5712, VIQR
-and windows-1258.  VSCII is deprecated in favor of TCVN-5712.  The
-Current setting gives higher priority to the coding system VISCII than
-TCVN-5712.  If you prefer TCVN-5712, please do: (prefer-coding-system
-'vietnamese-tcvn).  There are two Vietnamese input methods: VIQR and
-Telex, VIQR is the default setting.")))
+They can be decoded from and encoded to VISCII, VSCII-1 (TCVN-5712),
+VIQR and windows-1258.  The current setting gives higher priority
+to the coding system VISCII than VSCII-1.  If you prefer VSCII-1,
+please do: (prefer-coding-system 'vietnamese-vscii).  There are
+two Vietnamese input methods: VIQR and Telex, VIQR is the default
+setting.")))
 
 (define-coding-system 'windows-1258
   "windows-1258 encoding for Vietnamese (MIME: WINDOWS-1258)"
@@ -98,15 +101,6 @@ Telex, VIQR is the default setting.")))
   :mime-charset 'windows-1258)
 (define-coding-system-alias 'cp1258 'windows-1258)
 
-(define-coding-system 'vietnamese-tcvn
-  "8-bit encoding for Vietnamese TCVN-5712"
-  :coding-type 'charset
-  :mnemonic ?t
-  :charset-list '(tcvn-5712)
-  :suitable-for-file-name t)
-(define-coding-system-alias 'tcvn 'vietnamese-tcvn)
-(define-coding-system-alias 'tcvn-5712 'vietnamese-tcvn)
-
 (provide 'vietnamese)
 
 ;;; vietnamese.el ends here