A macro for shortening which-key descriptions

my-wk-abbrev.el

(defun my/wk-abbrev (prefixstr &optional prefixabbrev)
  "Remove PREFIXSTR from which-key descriptions.
Or, with PREFIXABBREV, replace it.  Optionally, condition replacement on
the value of MODE.  An `eval-after-load' is included, to ensure that
which-key will have loaded before adding to
`which-key-replacement-alist'."
  (let ((wkabbfuncsym (intern
                       (concat "my-wk-" prefixstr "-abbreviator")))
        (rx (concat prefixstr "-")))
    (setq which-key-replacement-alist
          (append
           which-key-replacement-alist
           (list
            (cons (cons nil rx)
                  (fset wkabbfuncsym
                        (lambda (wkcons)
                          (let ((inkey (car wkcons))
                                (indesc (cdr wkcons)))
                            (cons
                             inkey
                             (replace-regexp-in-string
                              rx (if prefixabbrev
                                     (concat "\\1"
                                             prefixabbrev "-")
                                   "\\1")
                              indesc)))))))))))

Example usage:

(use-package gnus
  ;; stuff here
  :config
  (my/wk-abbrev "gnus-agent"   "Ga")
  (my/wk-abbrev "gnus-server"  "Gs")
  (my/wk-abbrev "gnus-topic"   "GT")
  (my/wk-abbrev "gnus-group"   "GG")
  (my/wk-abbrev "gnus-article" "GA")
  (my/wk-abbrev "gnus-summary" "GS")
  (my/wk-abbrev "gnus-browse"  "GB"))

Updated and simplified for maintainability.