bug#57531: 28.1; Character encoding missing for "eo"

[Gregory Heytings]

> > To avoid such bugs, the most reasonable thing to do for users is to 
> > always specify the encoding.
>
> Should we perhaps have an entry in PROBLEMS with that information?

Would it not be better if Emacs checked the LANG environment variable on 
startup and warned the user when LANG does not specify an encoding?  Like 
this:

diff --git a/lisp/startup.el b/lisp/startup.el
index 50a8f491d8..338fb47f64 100644
--- a/lisp/startup.el
+++ b/lisp/startup.el
@@ -824,6 +824,14 @@ normal-top-level
        (unless inhibit-startup-hooks
          (run-hooks 'window-setup-hook))))

+    (when (< (length (split-string (getenv "LANG") "\\.")) 2)
+      (display-warning 'initialization
+                       (format "%s%s%s"
+                               "The LANG environment variable, set to `"
+                               (getenv "LANG")
+                               "', does not specify an encoding.")
+                       :warning))
+
     ;; Subprocesses of Emacs do not have direct access to the terminal, so
     ;; unless told otherwise they should only assume a dumb terminal.
     ;; We are careful to do it late (after term-setup-hook), although the