--text follows this line--

When melpa is included in the package archives and the package list is
being updated, the result depends on the language environment. Under
"English", everything works OK:

emacs -Q --eval '(progn (set-language-environment "English")(require (quote package))(add-to-list (quote package-archives) (quote ("melpa" . "http://melpa.org/packages/")))(package-list-packages))'

When the environment is set to "French" or "Czech", though, it fails with

Failed to verify signature archive-contents.sig:
Bad signature from 474F05837FBDEF9B GNU ELPA Signing Agent <elpasign@elpa.gnu.org>
Command output:
gpg: Signature made Mon 18 Mar 2019 10:10:04 PM CET using DSA key ID 7FBDEF9B
gpg: BAD signature from "GNU ELPA Signing Agent <elpasign@elpa.gnu.org>" [unknown]

At the same time, it asks for encoding:

These default coding systems were tried to encode "
(1 (zzz-t...":
   (iso-latin-2-unix (13884 . 37326) (13885 . 40165) (32038 . 248)
   (32095 . 248) (39468 . 234) (39539 . 234) (71321 . 248) (71399 .
   248) (71700 . 248) (71778 . 248) (72084 . 248))
However, each of them encountered characters it couldn’t encode:
   iso-latin-2-unix cannot encode these: 野 鳥 ø ø ê ê ø ø ø ø ...

Click on a character (or switch to this window by ‘C-x o’
and select the characters by RET) to jump to the place it appears,
where ‘C-u C-x =’ will give information about it.

Select one of the safe coding systems listed below,
or cancel the writing with C-g and edit the buffer
    to remove or modify the problematic characters,
or specify any other coding system (and risk losing
    the problematic characters).

   utf-8 gb18030 utf-7 utf-16 utf-16be-with-signature
   utf-16le-with-signature utf-16be utf-16le iso-2022-7bit utf-8-auto
   utf-8-with-signature utf-7-imap utf-8-emacs prefer-utf-8

Choroba

In GNU Emacs 26.1 (build 1, x86_64-pc-linux-gnu, Motif Version 2.3.4)
  of 2018-09-10 built on still
Windowing system distributor 'The X.Org Foundation', version 11.0.11803000
System Description:	openSUSE Leap 42.3

Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.
user-error: Beginning of history; no preceding item [2 times]
user-error: End of history; no default available

Configured using:
  'configure --with-kerberos5=yes --with-x-toolkit=motif --with-x=yes'

Configured features:
XPM JPEG TIFF GIF PNG SOUND DBUS GSETTINGS NOTIFY GNUTLS LIBXML2
FREETYPE XFT ZLIB TOOLKIT_SCROLL_BARS MOTIF X11 THREADS

Important settings:
   value of $LANG: en_US.UTF-8
   value of $XMODIFIERS: @im=local
   locale-coding-system: utf-8-unix

Major mode: Lisp Interaction

Minor modes in effect:
   tooltip-mode: t
   global-eldoc-mode: t
   eldoc-mode: t
   electric-indent-mode: t
   mouse-wheel-mode: t
   tool-bar-mode: t
   menu-bar-mode: t
   file-name-shadow-mode: t
   global-font-lock-mode: t
   font-lock-mode: t
   blink-cursor-mode: t
   auto-composition-mode: t
   auto-encryption-mode: t
   auto-compression-mode: t
   line-number-mode: t
   transient-mark-mode: t

Load-path shadows:
None found.

Features:
(shadow sort mail-extr emacsbug message rmc puny seq byte-opt gv
bytecomp byte-compile cconv cl-loaddefs cl-lib dired dired-loaddefs
format-spec rfc822 mml easymenu mml-sec password-cache epa derived epg
epg-config gnus-util rmail rmail-loaddefs mm-decode mm-bodies mm-encode
mail-parse rfc2231 mailabbrev gmm-utils mailheader sendmail rfc2047
rfc2045 ietf-drums mm-util mail-prsvr mail-utils elec-pair time-date
mule-util tooltip eldoc electric uniquify ediff-hook vc-hooks
lisp-float-type mwheel term/x-win x-win term/common-win x-dnd tool-bar
dnd fontset image regexp-opt fringe tabulated-list replace newcomment
text-mode elisp-mode lisp-mode prog-mode register page menu-bar
rfn-eshadow isearch timer select scroll-bar mouse jit-lock font-lock
syntax facemenu font-core term/tty-colors frame cl-generic cham georgian
utf-8-lang misc-lang vietnamese tibetan thai tai-viet lao korean
japanese eucjp-ms cp51932 hebrew greek romanian slovak czech european
ethiopic indian cyrillic chinese composite charscript charprop
case-table epa-hook jka-cmpr-hook help simple abbrev obarray minibuffer
cl-preloaded nadvice loaddefs button faces cus-face macroexp files
text-properties overlay sha1 md5 base64 format env code-pages mule
custom widget hashtable-print-readable backquote dbusbind inotify
dynamic-setting system-font-setting font-render-setting motif x-toolkit
x multi-tty make-network-process emacs)

Memory information:
((conses 16 95003 9709)
  (symbols 48 20225 1)
  (miscs 40 41 143)
  (strings 32 28261 1189)
  (string-bytes 1 743314)
  (vectors 16 13966)
  (vector-slots 8 491676 10904)
  (floats 8 51 66)
  (intervals 56 225 0)
  (buffers 992 11)
  (heap 1024 37756 1009))