Add rudimentary translation support

See #285.

lisp/transient.el

@@ -1572,6 +1572,8 @@ This is bound while the suffixes are drawn in the transient buffer.")
     mwheel-scroll
     scroll-bar-toolkit-scroll))
 
+(defvar transient-translation-function nil)
+
 ;;; Identities
 
 (defun transient-prefix-object ()
@@ -3706,8 +3708,9 @@ have a history of their own.")
 
 (cl-defmethod transient--insert-group :around ((group transient-group))
   "Insert GROUP's description, if any."
-  (when-let ((desc (transient-with-shadowed-buffer
-                     (transient-format-description group))))
+  (when-let* ((desc (transient-with-shadowed-buffer
+                      (transient-format-description group)))
+              (desc (transient--maybe-translate obj desc)))
     (insert desc ?\n))
   (let ((transient--max-group-level
          (max (oref group level) transient--max-group-level))
@@ -3921,6 +3924,11 @@ as a button."
       (transient--add-face key 'transient-mismatched-key))
      (key))))
 
+(defun transient--maybe-translate (obj string)
+  (or (and transient-translation-function
+           (funcall transient-translation-function obj desc))
+      string))
+
 (cl-defgeneric transient-format-description (obj)
   "Format OBJ's `description' for display and return the result.")
 
@@ -3933,7 +3941,8 @@ and its value is returned to the caller."
                        (if (= (car (transient--func-arity desc)) 1)
                            (funcall desc obj)
                          (funcall desc))
-                     desc)))
+                     desc))
+             (desc (transient--maybe-translate obj desc)))
     (if-let* ((face (transient--get-face obj 'face)))
         (transient--add-face desc face t)
       desc)))
@@ -3942,7 +3951,7 @@ and its value is returned to the caller."
   "Format the description by calling the next method.  If the result
 doesn't use the `face' property at all, then apply the face
 `transient-heading' to the complete string."
-  (and-let* ((desc (cl-call-next-method obj)))
+  (and-let* ((desc (transient--maybe-translate obj (cl-call-next-method obj))))
     (if (text-property-not-all 0 (length desc) 'face nil desc)
         desc
       (propertize desc 'face 'transient-heading))))