Update dinbrief class

Nowadays UTF-8 is standard, also port the features of the letter class
to dinbrief class.

---
 style/dinbrief.el |   45 ++++++++++++++++++++++++++++++++-------------
 1 file changed, 32 insertions(+), 13 deletions(-)

--- style/dinbrief.el
+++ style/dinbrief.el	2024-05-07 07:10:38.580274545 +0000
@@ -32,14 +32,26 @@
 (require 'tex)
 (require 'latex)
 
+;; Silence the compiler:
+(declare-function font-latex-add-keywords
+                  "font-latex"
+                  (keywords class))
+
+(defvar LaTeX-dinbrief-class-options
+  '("10pt" "11pt" "12pt" "norm" "a4paper" "a5paper" "b5paper"
+    "letterpaper" "legalpaper" "executivepaper" "twoside"
+    "addresshigh" "addressstd" "onecolumn" "twocolumn")
+  "Package options for the letter class.")
+
 (TeX-add-style-hook
  "dinbrief"
  (lambda ()
-   (add-hook 'LaTeX-document-style-hook
-             #'LaTeX-dinbrief-style)
    (LaTeX-add-environments
     '("letter" LaTeX-dinbrief-env-recipient)
     "dinquote")
+   (add-hook 'LaTeX-document-style-hook
+             #'LaTeX-dinbrief-style)
+   (setq LaTeX-default-document-environment "letter")
    (TeX-add-symbols
     '("address" "Absender")
     '("postremark" "Postvermerk")
@@ -61,7 +73,22 @@
     '("backaddress" "Retouradresse")
     '("signature" "Unterschrift")
     '("opening" "Anrede")
-    '("closing" "Schluss")))
+    '("closing" "Schluss"))
+
+   ;; Fontification
+   (when (and (featurep 'font-latex)
+              (eq TeX-install-font-lock 'font-latex-setup))
+     (font-latex-add-keywords '(("subject" "{")
+                                ("address" "{")
+                                ("signature" "{")
+                                ("opening" "{")
+                                ("closing" "{")
+                                ("location" "{")
+                                ("handling" "{")
+                                ("cc" "{")
+                                ("encl" "{")
+                                ("ps" "{"))
+                              'function)))
  TeX-dialect)
 
 (defmacro LaTeX-dinbrief-insert (&rest args)
@@ -78,16 +105,8 @@
     (open-line 2)
     (indent-relative-first-indent-point)
     (LaTeX-dinbrief-insert TeX-esc "usepackage"
-                           LaTeX-optop "latin1,utf8" LaTeX-optcl
-                           TeX-grop "inputenc" TeX-grcl)
-    (newline-and-indent)
-    (LaTeX-dinbrief-insert TeX-esc "usepackage"
-                           LaTeX-optop "T1" LaTeX-optcl
-                           TeX-grop "fontenc" TeX-grcl)
-    (indent-relative-first-indent-point)
-    (LaTeX-dinbrief-insert TeX-esc "usepackage"
                            TeX-grop "ngerman" TeX-grcl))
-  (TeX-run-style-hooks "inputenc" "fontenc" "ngerman"))
+  (TeX-run-style-hooks "ngerman"))
 
 (defun LaTeX-dinbrief-env-recipient (environment)
   "Insert ENVIRONMENT and prompt for recipient and address."
@@ -246,7 +265,7 @@
   (let ((ctime-string (current-time-string))
         (month-alist '(("Jan" . "Januar")
                        ("Feb" . "Februar")
-                       ("Mar" . "M\\\"arz")
+                       ("Mar" . "März")
                        ("Apr" . "April")
                        ("May" . "Mai")
                        ("Jun" . "Juni")