On Sun, Mar 21, 2021 at 03:18:40AM +0100, Emanuel Berg via Users list for the GNU Emacs text editor wrote:
> I do `lua-mode', then it says 'rx--translate-form: Unknown rx
> form ‘symbol’'
> 
> GNU Emacs 28.0.50 (build 1, x86_64-pc-linux-gnu, GTK+ Version
> 3.24.5, cairo version 1.16.0) of 2020-10-23

My hunch is that there's some rx form referring to a symbolic
rx (cf. [1]) named, appropriately `symbol' which it doesn't
find.

Possibly a botch in "your" lua-mode?

Sorry for not being more specific.

Cheers

[1] 34.3.3.3 Defining new ‘rx’ forms
    https://www.gnu.org/software/emacs/manual/html_node/elisp/Extending-Rx.html

 - t