@torounit You not only need to add $hook_extra to the method signature, you also need to pass it on to the 'upgrader_pre_download' filter within that method, so that it can serve its purpose.

@schlessera Thank you your reviewing !!
fixed filter parameter now.

Thanks for the PR, @torounit !

Hello, I still have this issue with WP-Cli 2.4.0.
I'm on MacOS Big Sur 11.1, PHP 7.4 (installed via homebrew).
I get this warning when updating languages :

PHP Warning: Declaration of WP_CLI\LanguagePackUpgrader::download_package($package, $check_signatures = false) should be compatible with WP_Upgrader::download_package($package, $check_signatures = false, $hook_extra = Array) in phar:///usr/local/bin/wp/vendor/wp-cli/language-command/src/WP_CLI/LanguagePackUpgrader.php on line 51

But everything updates smoothly, just a warning.

@nderambure Please see wp-cli/wp-cli#5494 (comment)

Thx @wojsmol, missed that one !

@torounit: In WP CLI nightly (2,5,x) the issue is indeed fixed (probably by this PR, right?). What still bothers me is the reason for why this issue occurred on some sites but no on other sites. The sites run on the same server and have the same WordPress core releases, the same languages should be installed and used, and the same WP CLI is used on workstation/client and server (2.4). So why does this warning/notice happens for one particular site, but not for other sites? Also it seems to happen when using a blank site and transferring the database over to it from the affected site.