Source

File: wp-admin/includes/class-plugin-upgrader.php

public function upgrade_strings() {
		$this->strings['up_to_date'] = __( 'The plugin is at the latest version.' );
		$this->strings['no_package'] = __( 'Update package not available.' );
		/* translators: %s: Package URL. */
		$this->strings['downloading_package']  = sprintf( __( 'Downloading update from %s&#8230;' ), '<span class="code">%s</span>' );
		$this->strings['unpack_package']       = __( 'Unpacking the update&#8230;' );
		$this->strings['remove_old']           = __( 'Removing the old version of the plugin&#8230;' );
		$this->strings['remove_old_failed']    = __( 'Could not remove the old plugin.' );
		$this->strings['process_failed']       = __( 'Plugin update failed.' );
		$this->strings['process_success']      = __( 'Plugin updated successfully.' );
		$this->strings['process_bulk_success'] = __( 'Plugins updated successfully.' );
	}