How do I enable speedbar to display all types of files?

For the sake of keep info updated, in my updated emacs: GNU Emacs 26.1 (build 1, x86_64-redhat-linux-gnu, GTK+ Version 3.23.2) of 2018-08-13

To get .files continuing be showed, now I have to set

all-types-of-files (custom-set-variables '(speedbar-show-unknown-files t) )

AND

(setq speedbar-directory-unshown-regexp "^\(\.\.*$\)\'")

learned from: https://emacs-devel.gnu.narkive.com/0k8PccN3/speedbar-and-dot-files

Ok this might sound kind of basic but, have you right-clicked on the speedbar and checked 'Show all Files'? Otherwise, you should update the speedbar buffer by pressing 'g'.

There should be something like this on your emacs, though this is not usually set up by hand.

(custom-set-variables
 '(speedbar-show-unknown-files t)
)