Plugin_Upgrader::install

				$this->strings['installing_package'] = __( 'Updating the plugin…' );
				$this->strings['process_failed']     = __( 'Plugin update failed.' );
				$this->strings['process_success']    = __( 'Plugin updated successfully.' );
			}

			if ( 'downgrade-plugin' === $this->skin->overwrite ) {
				$this->strings['installing_package'] = __( 'Downgrading the plugin…' );
				$this->strings['process_failed']     = __( 'Plugin downgrade failed.' );
				$this->strings['process_success']    = __( 'Plugin downgraded successfully.' );
			}
		}
	}

	/**
	 * Install a plugin package.
	 *
	 * @since 2.8.0
	 * @since 3.7.0 The `$args` parameter was added, making clearing the plugin update cache optional.
	 *
	 * @param string $package The full local path or URI of the package.
	 * @param array  $args {
	 *     Optional. Other arguments for installing a plugin package. Default empty array.
	 *
	 *     @type bool $clear_update_cache Whether to clear the plugin updates cache if successful.
	 *                                    Default true.
	 * }
	 * @return bool|WP_Error True if the installation was successful, false or a WP_Error otherwise.
	 */
	public function install( $package, $args = array() ) {
		$defaults    = array(
			'clear_update_cache' => true,
			'overwrite_package'  => false, // Do not overwrite files.
		);
		$parsed_args = wp_parse_args( $args, $defaults );

		$this->init();
		$this->install_strings();

		add_filter( 'upgrader_source_selection', array( $this, 'check_package' ) );

		if ( $parsed_args['clear_update_cache'] ) {