wp-admin/includes/class-language-pack-upgrader.php:325Checks that the package source contains .mo and .po files.
$sourcestring|WP_Error$remote_sourcestringstring|WP_Error public function check_package( $source, $remote_source ) { global $wp_filesystem; if ( is_wp_error( $source ) ) { return $source; } // Check that the folder contains a valid language. $files = $wp_filesystem->dirlist( $remote_source ); // Check to see if the expected files exist in the folder. $po = false; $mo = false; $php = false; foreach ( (array) $files as $file => $filedata ) { if ( str_ends_with( $file, '.po' ) ) { $po = true; } elseif ( str_ends_with( $file, '.mo' ) ) { $mo = true; } elseif ( str_ends_with( $file, '.l10n.php' ) ) { $php = true; } } if ( $php ) { return $source; } if ( ! $mo || ! $po ) { return new WP_Error( 'incompatible_archive_pomo', $this->strings['incompatible_archive'], sprintf( /* translators: 1: .po, 2: .mo, 3: .l10n.php */ __( 'The language pack is missing either the %1$s, %2$s, or %3$s files.' ), '<code>.po</code>', '<code>.mo</code>', '<code>.l10n.php</code>' ) ); } return $source; }Introduced in 3.7.0. Unchanged from 6.7.7 through 7.1.0.
Signature, return type and hooks compared across 5 parsed releases.
src/wp-admin/includes/class-language-pack-upgrader.php, and regenerated for each WordPress release so it tracks the code rather than a snapshot of it.