0. emacs -Q
1. M-x calendar RET
2. 'g d' (calendar-goto-date)
3. type any year and RET
4. on the prompt "Month name: " type TAB

Month names are sorted alphabetically that makes no sense:

  April August December February January July
  June  March  May      November October September

What is worse is that currently it's impossible to customize
this sorting order.

This was discussed recently in
https://lists.gnu.org/archive/html/emacs-devel/2023-11/msg01233.html

Here is a patch that allows such customization

 (setopt completion-category-overrides
         '((calendar-month
            (display-sort-function . identity))))

that will sort month names chronologically:

  January February March     April   May      June
  July    August   September October November December